this has happend to me before, and i think this is how i fixed it...

when its booting up keep pressing f8 to get to the boot up selection menu. select safe mode and see if it boots up, then try opening restore and go back a week or so.. maybe it will replace the system file...

last easy solution would be to stick that hard drive into another computer as a slave drive and get all your information off it before you format and install...

you might have to reset folder permission settings if you get "not accessable" error when opening your "my documents" folder...