COMPUTER MALWARE

"Out of the blue" I got all sorts of pop-ups to the fact that I have just become infected with a bunch of viruses, etc. The pop-up gave me 2 or 3 choices - but looked very suspicious & no matter what "button" I pushed it brought me back. The Windows "shield" was displayed everywhere. I tried to go to the windows site, but couldn't - so I turned the computer off. When I turned it back on my Start Page appeared, but as soon as I touched anything I got a message that something had blocked the program. How do I get in touch with Internet Explorer? I tried with another server, but the message was to the effect that I had to use Internet Explorer. I think it is clear that I have a virus of some kind. Also, I have tried to install Service Packs 1 and 2, but they didn't take.