Ivor's suggestion might well do the trick. (It's got me out of trouble often enough!). Otherwise . . .
Try restarting the laptop in Safe Mode (which is usually achieved via pressing F8 during the boot process). Don't panic if you find your screen looks odd; that's just because the video driver won't have loaded.
Then run System Restore (from Start > All Programs > Accessories > System Tools > System Restore) to take the registry back to a date when your laptop was functioning normally.