Windows wont shutdown or restart

i have windows xp pro sp3. i have encountered this problem recently, i've been on vacation so i cant really remember when exactly it started or if i did something to cause it. the problem is, every time i go to either restart or shutdown my system, windows begins to shutdown normally, even going as far as the signature windows shutdown chime, and "windows shutting down" screen, but when the sytsem should be cutting off or posting, it just goes to a blank blue screen. no error message, no BSOD, just a blank blue screen, and it will stay on the blue screen forever as far as i know(the longest time probably around 12 hours) unless i manually reset it. everything else runs fine.

the only problem i can think of that might have something to do with this is, i did have some virus problems, i left town for a week or so a while back and came back to find my computer infected very badly. i had it unplugged the whole time. i got all the viruses fixed, with the exception of one, Win32.Delf.uc. spybot says it fixes it, but when i restart windows and re-scan, it shows up again. this is what im working with:

core 2 duo e8400
gigabyte ep45-ud3r mob
2 gigs of piq ddr2 800
radeon hd4770
WDC 500gig HD

avast pro 4.8 anti virus
comodo firewaill
spybot
malwarebytes

any help would be appreciated, thank you