System Protection (aka System Restore in Windows XP) literally turns back time for your computer - it restores the system files, programs, drivers and settings that were used at the time when your computer was still working well.
Do not worry, System Protection/Restore will not touch your documents, e-mails, pictures, videos, etc. It will restore only system and program files, and settings in Registry. But if you have installed a program after the time you want to restore your system to, you will still have to reinstall that program.
System Protection also restores your previous Windows password in case you changed it recently - so please make sure you remember your previous password!
It is preferred to start System Restore while Windows runs in normal mode unless your device runs Windows 10.
While System Restore can be used in Safe Mode (including Safe Mode with Command Prompt), you cannot revert the action in Windows Vista, 7 or 8/8.1.
Some versions of Windows 10 have problems with System Restore, causing boot error 0xc000021a.
If Windows runs normally while you start a system restore, you can always undo it. Using Safe Mode or Windows RE disables the undo function.
In case Windows is unable to start or run normally, use one of the following options to start System Restore:
- Boot into Safe Mode and run System Restore. In Windows XP, this is the only alternative.
- If Windows fails to start in Safe Mode, boot into Recovery Environment (instructions for Windows Vista and 7; instructions for Windows 8/8.1 and Windows 10) from Windows installation media or System Repair Disc (Windows 7) or Recovery Drive (Windows 8, 8.1 and 10).
- To start System Restore from Command Prompt or Run dialog, type rstrui.exe, and press Enter.
Never expect System Restore to remove a virus, rootkit or any other malware!
Steps to try before using System Restore
- Last Known Good Configuration often solves booting and stability problems after installing software, drivers, or messing with Registry entries. This is available for Windows XP, Vista and 7 only.
- Always boot to Safe Mode at least once - this often repairs corrupted file system and essential system files.
- If Windows is able to boot, use System File Checker and icacls.exe to repair corrupted system files. If Windows starts and runs properly only in Safe Mode, use it to enable Clean Boot mode for troubleshooting third-party (non-Microsoft) software and drivers.
- While Windows is running, use free WhoCrashed for determining BSOD (Blue Screen Of Death) causes.
In Windows Vista and later, Reliability Monitor might also reveal faulty drivers or software.
Restoring to an earlier point with System Restore
In Windows XP, open Start menu and browse to All Programs, Accessories, System Tools. Click System Restore.
In Windows Vista and 7, click Start button or press Ctrl+Esc on your keyboard, type "system restore" into Start menu Search box and click System Restore.
In Windows 8 and 8.1, use the keyboard shortcut Windows Key+W to open Settings Search, type "system restore" into the Search box and click Create a restore point. That's correct, this just opens the System Protection window and does not create a new restore point.
In Windows 10, it is recommended to boot into Windows Recovery Environment and run System Restore from there. This prevents the boot error 0xc000021a from happening.
Alternatively, open Start menu or Cortana keyboard search (Windows Key+S), type "system restore" and click Create a restore point.
In Windows 8/8.1 and 10, you must also click the System Restore button in System Protection tab of the System Properties window. If the tab is not available, open Command Prompt or Run dialog (keyboard shortcut Windows Key+R), type rstrui.exe and press Enter or click OK.
If you have no restore points available or System Protection is turned off, you are out of luck with System Restore. This might be caused by some malware disabling System Restore completely.
If you have several versions of Windows (for example, Vista and 7) installed on the same drive or partition, then starting one Windows version deletes all restore points for other versions - Microsoft decided to implement it so that the same folder is used for storing Restore Points.
If you do have something to restore, you will be reminded that System Restore will not affect your documents, e-mails or other personal data - just programs and their settings will be restored. Click Next.
In Windows 8, 8.1 and 10, if you launched System Restore from Recovery Environment and there are System Restore Points available, Windows will ask you to sign in first. Click your user name, provide your password and click Continue. Please note that U.S. keyboard layout is active by default, so use the Change keyboard layout button if necessary.
In Windows XP, a calendar appears. The dates that are in bold have available restore points. Select the one you need and click Next.
In Windows Vista, a list of all available restore points is displayed. Select the one you need and click Next.
In Windows 7, 8, 8.1 and 10, only recent Restore Points are displayed by default. If you need to recover an older one, tick the Show more restore points check box.
To see which programs will be affected by restoring to an earlier restore point in Windows 7, 8/8.1 or 10, click the one you want to restore in the list and then click Scan for affected programs. Building the list will take a while.
Check the Programs and drivers that will be deleted list and the Programs and drivers that might be restored lists. Please note that restoring a program does not always mean that it will start or work correctly - you might still need to reinstall some software. Click Close, choose your restore point and then click Next.
A summary screen appears. Click Next or Finish.
In Windows XP, ignore warnings about the drives where System Restore was turned off.
In Safe Mode of Windows Vista and newer, System Protection warns that the restoration cannot be undone. Click Yes to start restoring. This warning does not appear if you start System Restore while Windows runs normally (and you can undo the restore).
If started from Windows normal mode, the restoration process usually logs all users off and the message "Windows is shutting down" might be displayed. Do not worry, System Restore just needs to unlock files and settings before it can run properly.
The restoration process takes time - from ten minutes to several hours is absolutely normal.
Do not reboot or power off your computer during the restoration process!
First, System Restore initializes and restores Windows files and settings (no, your documents are not affected), then it will clear temporary files.
After System Restore is complete, your computer will restart. In Recovery Environment, an additional dialog will be displayed, click Restart.
If Windows starts and runs normally now, then the restoration probably solved your problem. Please note that the restart and logging on after System Restore might take noticeably longer than usual - this is normal just this once.
If Windows will not restart your computer automatically in three hours, verify that the hard disk activity indicator light is not on and does not blink within a minute. You can then press the reset button or hold down the power button for more than 10 seconds to reboot or turn off your PC. After turning off, wait 20 seconds and turn the computer back on.
Windows should start normally and System Restore was probably not interrupted.
Log on as usual and you will hopefully see a System Restore success dialog. Click Close. In Windows 8 and 8.1, the dialog appears only if you open Desktop (Windows Key+D).
If the restoration affected programs or drivers, you might need to reinstall them - but make sure that they are not the cause of your Windows problems! Reinstall one of the programs or drivers and then restart to see if Windows works correctly. Then continue with reinstalling the second one, restart again, etc. Welcome to the world of troubleshooting! 
If System Restore fails
If System Restore did not finish its job well enough, you will see an error message after logging on to Windows. Read the Details part carefully - this includes the probable cause of failure.
Here system was rebooted during restore (you should never do that while restoring!). Click Home or Run System Restore to retry restoring to an earlier point of time.
Here System Restore was not able to access some file or files. Although the details part talks about anti-virus programs, the real cause was that files or folders were messed up on hard disk drive. You should boot into Safe Mode then because a disk check is always performed before starting Windows in that mode. Then restart your device and retry System Restore in normal mode.
Click Close in such case.
Undoing a System Restore operation
If restoration itself succeeds, but you have even more problems than before, you might be able to undo the last System Restore operation. In Windows Vista, 7, 8/8.1 and 10, you can use the undo feature only if you ran System Restore in the normal mode of Windows (not Safe Mode). In other cases, just restore some other restore point available (described here).
To undo the last restoration, run System Restore again:
- In Windows XP, open Start menu and browse to All Programs, Accessories, System Tools. Click System Restore.
- In Windows Vista and 7, open Start menu and type "system restore" into the Search box. Then click System Restore in search results.
- In Windows 8 and 8.1, open Settings Search using keyboard shortcut Windows Key+W, type "system restore" into the Search box and click Create a restore point. In System Properties window, click System Restore.
- In Windows 10, open Start menu or Cortana search, type "system restore" and click Create a restore point. In System Properties window, click System Restore.
If System Restore detects a previously restored state, you have an option to undo it.
Select Undo my last restoration (in Windows XP) or Undo System Restore. Then click Next.
In Windows XP, ignore all warnings about disks that had System Restore turned off.
Click Next or Finish to start undoing.
In Windows Vista, 7, 8/8.1 and 10, a warning about interrupting System Restore appears. Click Yes.
You will again be logged off and System Restore will take from 10-30 minutes to several hours. After Windows starts again, log on and check that you see success message about System Restore Undo.