This is most likely the same issue as what's in your other thread. So I would concentrate on your other one.
As a McAfee person is dealing with you there I'll offer some suggestions. Can you get into the machine by booting into "Safe Mode with Networking"? (Reached by tapping F8 repeatedly while booting up and selecting that item from the list).
If so try running McAfee VirusScan in Safe Mode by going to My Computer (XP) or Computer (Vista/Win 7) and right-clicking the hard drive and selecting "Scan".
It will take a while and all you'll see is the taskbar icon. Hovering over it will give a progress report.
If that fails, in the same mode ("With Networking" gives you internet access in Safe Mode) go here and download the free version of Malwarebytes. Still in that mode install it and update it, then run a complete scan and let it delete anything it finds. Reboot when asked and hopefully you'll have your machine back.