Spyware issues - cannot run cmd or regedt32, SD, MalwareBytes, Ad-Aware, Norton AV not helping Options

[Jeff Melnik]

Recently cleaned off the fake spyware removal program SpyWare Protect 2009 with info found on this site - thanks!

However, still having the following symptoms of something still wrong on my computer:
- Norton AntiVirus has been detecting a Backdoor Trojan virus of some kind popping up - setup_u.exe. It does get quarantined - yet it seems to keep coming back.
- After running a Google search, when clicking on a link in the search results the browser (FireFox or IE) sometimes gets "hijacked" and brought to a separate site - usually some type of advertisement. Clicking the back button and re-clicking on the search result then gets me to the site I'm supposed to go to.
- Ad-Aware, Spybot SD, and Malwarebytes are all finding NOTHING.
- It would seem there is a registry entry I need to delete to clean this up, but I have found that I now can not run cmd.exe or regedt32.exe. MS Installer seems to be having issues as well, so I'm having trouble getting alternative scanning software to use to see what's going on. Was going to try re-installing the Installer based on Symantec recommendations, but when I try to move the old files by renaming them, the files keep coming back, almost as if I did a copy.

Per the prep guide, I downloaded DDS.scr and tried running it - but nothing happens (a command window opens for a fraction of a second, but it is blank, and then goes away before I can even blink), so unfortunately there is no output to attach here. So I guess the first thing would be if someone could tell me how to get DDS.scr to work, or has any idea what is going on based on what I am describing above.

Alternatively I could supply the TrendMicro HijackThis log, but I'll wait for some feedback first.

Thanks in advance for your assistance.