|Does it do the same when you are in Windows Safe-Mode ????|
If Safe-Mode works,
Try System Restore to a date when all was good.
Start >All Programs >Accessories >System Tools
Using System Restore too many times can cause
more harm than good. After doing a restore
that does not fix a problem, then UNDO the
Restoration, and try another restore point, or
just do the UNDO.