Full Of Trojan Horses

My computer became full of malware - I had thought I had cleaned it out with Norton, Adaware, and windows spyware removal, however, when I turned the computer off and turned it back on, it is not working. It will load in normal mode, though I can't access any programs. I try to load in Safe mode, but it goes to a black screen and continually is loading. Anything I can do? I want to download the Highjackthis program, but can't seem to be able to do anything. My machine runs on Windows XP Media Center Service pack 2. Any help to get me started is appreciated!

Hello and welcome to the forum. Sorry about the delay in responding If you still need help let me know.