problems with malware removal...help!!!

I am trying to go through the malware removal procedures posted on this site. I first noticed a problem with my PC running VERY much slower than usual, and I tried to go to the lavasoft webpage to get adaware to try to find malware, but after I click on the lavasoft link or type the address in the address bar, the browser just disappears off the screen (tried both firefox and IE). So I came here and followed the malware removal procedures, but when I try to download SUPERantispyware, the download progress window disappears. Spybot S&D downloads, but the install progress window disappears when I get to that point. This is bad. Please help???