I need the exact error message please, and if you have an event viewer warning or error please copy/paste that error in your next reply.
you can click on the third icon down, on the right in event viewer, this will copy the dialog to clipboard and then you can right click>paste in your reply.
also what is your os, Home, Pro, or media center edition??
are you fully updated from Microsoft updates??
what is your current antivirus??