Have you tried doing a scan in Safe-Mode? As well, what about an online scanner like:
Trend Micro
Pandasoft
Symantec
There are several are other possibilities - but these should be of use. The reason they and a Safe-mode scan may be of more use is if the malware/trojan is in residence, it cannot be removed easily. When you do a Safe-mode scan, make sure you disable System Restore - I suspect this may also be apart of the problem. Whatever you have is hiding out :?