My laptop is running Vista 64 bit and is a year old Dell. I downloaded something (can't recall what). I kept getting a message that the anti-virus program (McAffee, I think) quarantined something that could not be cleaned. I got a message that this is what was done. Every time I closed the message it reappeared a moment or two later. I decided that I would reboot the computer. It would not shut down so I cut off the power supply. In starting (after selecting to start normally) it will go to a screen that is largely black and has "Microsoft Corporation" at the bottom with a running scale above that. The scale moves just for a moment before freezing. Any ideas?