Just a thought as this happened to me about 3 years ago. I had no anti-virus s/w on my PC and unknown to me, I received via e-mail a worm virus. Clever little sod, every few minutes when powered up, I got the login box encourageing me to go online. When I did, I tried to go to ANY of the anti-virus s/w houses, Symantec, McAfee etc, etc the line dropped IMMEDIATELY. It would NOT let me view any of these sites in case I got anti-virus s/w.
I ended up formatting the h/d and got rid of the virus that way.