Hello Daniel,
There are few things that you can do to help get ride of a hard to find infection.
First thing I would do is run a scan in safe-mode.
Make sure you have the latest definition files, boot into safe mode and run a Disk Cleanup (right-click the C drive, Properties, Disk Cleanup) - that will delete all the files that are in these temporary locations, as well as IE's temporary files, etc. Then perform a full system scan in safe mode.
If that fails to detect and remove the threats, try the Norton Power Eraser.
http://security.symantec.com/nbrt/npe.asp?lcid=1033&origin=default
Because the Norton Power Eraser uses aggressive methods to detect these threats, there is a risk that it can select some legitimate programs for removal. You should use this tool very carefully, and only after you have exhausted other options.
Try these things and let me know how it goes for you.
Best,
Thomas