Trojan virus. Help!

Earlier this week I got myself a little trojan virus. I cleaned it up with Symantec Endpoint protection and spybot search and destroy and thought that was that. Unfortunately that was not that at all and the thing is multiplying. I've been seemingly lucky so far, the only noticable side-effect is that sometimes my computer is unable to start up but I know that it's probably doing things I haven't detected yet. Can anyone help me get rid of this thing? I'm running Windows 7 and 64-bit OS.

 

I'm not sure if this will be useful, but here is a list of the viruses Endpoint found:

Trojan.gen

Trojan.gen.2

Downloader

Trojan.malscript