You need Check Disk (a GUI version of command-line tool chkdsk) when there are errors on hard drives or external drives. Such errors can cause stability problems and even loss of data in worst cases.
Disk checking/chkdsk in Windows is able to repair file system errors (files messed up on the disk) and recover data from bad/unreadable clusters.
Windows 8, 8.1 and 10 are much more intelligent in detecting file system errors (they also inform you in Action Center with the "Restart to repair drive errors" notification) and they always repair them at startup (if you start or restart your computer). For hard drives, this means that in most cases no additional checks are required. You can still use Check Disk for detecting and fixing error on removable drives.
In case Windows is checking a drive at startup, please let it finish - the check might take up to half an hour. Usually, it takes much less time, but rebooting while a drive check is in progress might mess files up even more, or result in an unbootable state.
Open (My) Computer or This PC from Desktop or Start menu/screen. Alternativelty, press Windows KEY+E on your keyboard to launch Windows/File Explorer and navigate to Computer/This PC if necessary.
To check the drive where Windows is installed, right-click on an item that ends with "(C:)", for example Local Disk (C:) or Windows (C:). In Windows Vista, 7, 8, 8.1 and 10, the drive also has a small Windows logo (a four-color flag or a blue flag) on it. The drive might also end with "(D:)" or "(E:)" in case you have multiple operating systems installed. The drive or partition Windows is installed on is called System drive.
All hard disk drives, SSD-s and removable drives must contain at least one formatted partition/volume to become usable. System drives usually contain multiple partitions. Windows assigns each partition a different drive letter, such as C:, D:, E:, etc. Some partitions, such as Recovery Environment (RE) in Windows Vista and later do not have a drive letter and are therefore not visible in Windows/File Explorer. You can see these partitions in Disk Management or by using command-line tool named diskpart.
Drive letters A: and B: were usually reserved for floppy disk drives (FDD, often called "floppy") in older Windows versions, but you can still assign them to another drive/partiton . Please see Disk Management tutorial for more information.
In case your PC has more than one hard disk/SSD or partition/volume, repeat the following steps for other items, too. You can also check file system health of removable drives (USB sticks, external drives, SD/MMC/CF cards, etc), but you do not need to check optical media (CD-s, DVD-s, Blu-Ray discs).
Choose Properties from the menu.
Open Tools tab and click Check Now in the Error Checking section. In Windows 8, 8.1 and 10, this is called just Check.
In Windows Vista, User Account Control will open. Click Continue.
In Windows XP, Vista and 7, Check Disk dialog opens, choose Automatically fix file system errors and then click Start button. If you want to perform an exhaustive disk check, also activate the Scan for and attempt recovery of bad sectors option. Please note that this test might take several hours to complete.
In Windows 8/8.1 and 10, usually a "You don't need to scan this drive" dialog appears (you would have seen the "Restart to repair drive errors" notification from Action Center if the drive's file system was in bad condition). For system drive, click Scan drive to double-check; for other drives, click Scan and repair drive.
If Windows 8 or later already knows there are problems with the disk (the drive is marked "dirty" and there are events with ID 7 or 55 in Event Logs), "Repair this drive" dialog appears instead. Click Repair drive.
If this is your second or third hard disk in Windows XP, Vista and 7, the disk check will usually be performed right away. Windows 8 and newer will always run a check, even on system drive.
Windows XP always opens the "Disk Check Complete" message after the process is complete. Click OK.
Windows Vista, 7, 8/8.1 and 10 provide information on whether the scan found any errors. If the message says "Your device or disk was successfully scanned", there were no problems found and you can click Close.
In case the message is "Some problems were found and fixed" in Windows Vista and later, you can click the See details button or Show Details link to find out what exactly was repaired. In Windows 8/8.1 and 10, this opens Application log of Event Viewer, with event filter for Event ID 26226 applied.
Or just click Close if technical details are of no interest to you.
If this is your only hard disk partition/volume or the one that has Windows installed on, you'll see a warning that the disk/drive cannot be checked or repaired while it's in use. This happens because many files are locked and cannot be tested while Windows is running.
In Windows XP, click Yes to schedule a disk check for the next restart.
In Windows Vista and 7, click Schedule disk check.
In Windows 8/8.1 and 10, click Restart and repair now.
Restart your computer now to let the check run.
After restarting, a screen stating "A disk check has been scheduled" appears. You can cancel the boot-time check by pressing any key on your keyboard within the next 10 seconds (or 3 seconds in Windows 8 and later).
But this is not what we want, right? Stand by and see how Windows checks and repairs the drive.
It usually takes some time until the disk check completes. If you have a large hard drive full of data, the check might take even half an hour or more. In case you scheduled a complete disk check with testing for bad clusters, the test will probably run for several hours.
If only minor inconsistencies were found and repaired, Windows XP, Vista, 8/8.1 and 10 will start. In case of major problems resolved, a restart will be performed.
Windows 7 will always restart your computer after a disk check.
In case Disk Check could not fix all file system problems in one run, the testing and repairing process will start over after the restart. Please let it finish (your computer might be restarted again) and wait for Windows to start - it is very important that your hard disk is working properly. In worst cases, it takes up to three restarts to get rid of all errors.
In case bad clusters are detected on a hard drive, it is time to fully back up your most important data or the whole contents of the drive (the latter is called disk imaging). If the drive is not covered by warranty, you need to buy a new drive ASAP and replace the current one. Bad sectors tend to expand quickly, so please do not risk losing all your documents, photos, videos, etc!
Do not forget to check other drives or partitions, too!
The previous steps launched or scheduled a tool called chkdsk. However, if you need to quickly check current drive status or cancel a scheduled disk check, there is a command-line tool called chkntfs.
As the "ntfs" part hints, this tools works only with NTFS-formatted drives/partitions.
To use the chkntfs tool, launch elevated Command Prompt.
In Windows XP, if your account has administrative rights, you only need to click Command Prompt in Start menu, All Programs, Accessories. If you work with a standard/limited account, right-click Command Prompt, choose Run as and fill in administrator account name and password.
In Windows Vista, 7, 8/8.1 and 10, open Start menu or Start screen, type "cmd" without quotes, right-click the result and choose Run as administrator. Touch screen users in Windows 8 and newer should swipe in from the left side of screen and tap Search first.
In Windows Vista and later, User Account Control wakes up. Click Continue or Yes if your account has administrator's rights, or fill in administrative account user name and password.
First, let's check the status of a drive. Type chkntfs <drive letter to check>: , for example chkntfs C: (note the colon after drive letter) and press Enter key once. All chkntfs commands take only about a second to complete unless there are major issues with a drive.
If the drive's file system is fine, "is not dirty" is displayed in the results. This means that no further action is required.
However, if file system problems have been detected, "is dirty. You may use the /C option to schedule chkdsk for this drive" appears in the results. Please note that even if a disk check has already been scheduled for the dirty drive, this does not reflect in the results.
In case of a dirty drive, type chkntfs /C <drive letter>: , for example chkntfs /C C: and press Enter. The tool does not display a thing, but it is now time to restart your PC and let disk check run.
If the tested drive is not marked dirty, but a disk check has been scheduled for the next startup, the "Chkdsk has been scheduled manually to run on next reboot on volume" message informs of this.
The scheduled test might be necessary if you want to check for bad clusters, but in case you do not want the check to run, type chkntfs /X <drive letter>:, for example chkntfs /X C: and press Enter. The result only lists the file system type and nothing else.
Please note that this command actually excludes the drive from all further default boot-time checks, even if the drive will be marked dirty. Always follow the previous command with chkntfs /D command that restores the default behavior for all drives - but it does not restore the manually scheduled check you cancelled before. The latter command has no output again, so there is no screenshot included for it.
Final note: chkntfs schedules a default boot-time check, so if a drive/volume has not actually been marked dirty, the test will be skipped during the next reboot.
To turn on a drive's dirty bit in elevated Command Prompt, type fsutil dirty set <drive letter>: , for example fsutil dirty set C: and press Enter. This will force the automatic disk check to run even without using the chkntfs /C command. Action Center in Windows 8/8.1 and 10 will also pop up a "Restart to repair drive errors" message about a drive requiring boot-time check after turning on the dirty bit.