As I said above, if you haven't already, do a spyware/malware scan on that puter. I had the same problem last night (one of my daughters downloaded "bargan buddy" that got by Norton and MS spyware Beta? No!!! They disabled both to download an attachment from an email which was blocked by Norton 2005 and then re-enabled both (they are both banned from my puter now and they can screw upther own!) Tried to shut down and I just sat there...Nada!!! Ran MS spyware and found the Spyware program and deleted it and cleaned the registry. This is one good reason not to leave your puter on 24/7 if you have children!!! :0
Noli Nothis Permittere Te Terere!!
EVGA 680i, Dual EVGA 8800GT'S (650/950), 4 gigs OCZ DDR2 1066, Intel Q9450 at 3.8 Ghz, Koolance Water Cooled, Dual Plextor16x DL DVD+/-RW. Dual WD 250gb 16mb Cache Sata 3.0. 3DMark06 score = 19,168.