If you are running vista or windows 7 you can run the repair my computer, pre boot, press F8 until an advanced menu comes up, it may try to auto fix, i normally cancel that, then tell it to do a system restore before you got the virus, if that gets you in, run hitman pro, malware bytes and combo fix, also scan with avast, then do a boot time scan in avast. if that does not get you into windows i would run a hard drive test, pre boot. seatools for dos, burn to a cd from a different computer and boot to it, many computers use F10 to choose boot option, choose your cd/dvd drive. i hope this helps.
ART Computer Maintenance and Repair