If you do not have a fast computer or graphics adapter, you can disable some or all visual effects in Windows to make your computer more responsive.
Use keyboard shortcut Windows Key+Pause/Break to open System Properties.
You can also right-click My Computer or Computer on Desktop or in Start menu and select Properties.
In Windows Vista, 7 and 8, click Advanced System Settings on the left.
User Account Control will open. Click Continue or Yes.
In System Properties window, make sure Advanced tab is open. Click Settings button in Performance section:
In Visual Effects tab of Performance Options window, click Custom. Then deselect the following items to disable some unnecessary eye candy:
- Animate controls and elements inside windows (only in Windows Vista, 7 and 8)
- Animate windows when minimizing and maximizing
- Animations in the taskbar and Start Menu (Windows 7) or Animations in the taskbar (Windows 8)
- Fade or slide menus into view
- Fade or slide ToolTips into view
- Fade out menu items after clicking
- Save taskbar thumbnail previews (Windows 7 and 8)
- Show window contents while dragging
- Slide open combo boxes
- Slide taskbar buttons (only in Windows XP and Vista)
- Smooth-scroll list boxes
Then click OK twice to close Performance Options and System Properties and for changes to take effect:
You now have some processor-intensive animations and effect disabled while still having a modern Windows look retained.
Disabling all effects and using Windows Classic mode for best performance
If you have a really slow computer, you can try Windows Classic mode that looks a lot like Windows 2000 or Windows Me. This disables Windows themes, all visual effects and font smoothing. You will still have a modern Windows Start menu, but it looks... umm... old. 
In Windows 8, this actually has very small effect on how program windows, Metro applications, Start screen and Desktop look - it is still almost the same (fonts might get a bit blurry), but without eye candy.
To enable the classic look and bump performance up, select Adjust for best performance in Performance Options window, Visual Effects tab.
This is what different versions of Windows look like while using Classic look. Windows 8 is not displayed, as there are no really important changes.
