Try toggling the F8 key when you first turn on the computer. Do not quit until the Start-up page shows. The start-up page will allow you to boot into "safe Mode" when in safe mode go to Start > programs >acccessories > system tools > system restore.....while in system restore choose to restore to a DATE prior to your having trouble with your computer and restore to that date.

If that doesn't work then post back and we will try another avenue to get you up and running!