My god whatever you have... please don't spread it around. If you have done all of that and cannot find the problem then I would say that the software you used isn't doing what its suppose to be doing.
Try PestPatrol, or Stinger... let me the Stinger link... it looks for trojans and kills them.
http://vil.nai.com/vil/stinger
I would also ditch your viruse protection and try using McAfee or even *shudder* Nortan. You can also do an on line scan using Pandasoft.
http://www.pandasoftware.com/products/ActiveScan.htm
Good luck.