Possible causes:
-Accidently removing Windows hibernation files
-Power settings
-Incompatibility issues with video card and Vista
Possible solutions:
-Accidently removing Windows hibernation files (Soltion):
See:
http://support.microsoft.com/default.aspx/kb/929658 (This will explain how
to fix the hibernation issue in Vista if the hibernation files were
accidently removed through Clean-Up)
-Power Settings (Solution):
You may need to change your current power settings:
See:
http://windowshelp.microsoft.com/Windows/en-US/Help/d48c9f1d-2e69-4e6d-b949-5c4df1b0b9f91033.mspx
-Incompatibility issues with video card and Vista(Solution):
Check to make sure your computer graphics card is compatible with Windows
Vista. If you upgraded your computer to Windows Vista (Any edition) you may
need to re-install your current video card driver. To do this, insert your
monitor's or video card installation disk. If the hardware did not ship with
a disk, contact the manufacturers website.
*If your computer was shipped with Vista pre-installed, and your version is
validated, you may not have this problem*
I hope this helps
-Kirk