I got hit bad by a data-ransoming Trojan made by some branch of the Russian Cybermaffia, and subsequently with a Trojan that gave a false-positive virus scan message, locked down Firefox or IE, and tried to reroute me to fake webpages where I would DL more viruses. AVG, Spybot, and so on didn't even see them.
I was able to boot in Networking Safe-Mode, and download
Malwarebytes Anti-Malware. It's the only freeware package I've heard of that can deal with the heavy-hitters like the friggin
Vundo Trojan.
Alternatively, if you trust your own judgement, and can deal with potentially damning your computer, run a search for the suspicious processes on
Windows File Info or Google, and snag a
File Unlocking Utility that will let you halt, free up, and delete processes, programs, and viral .DLLs that are giving you shit.