I just pulled a virus out of a machine with exactly the same symptoms, plus a few.
The virus was W32/PEPatch. Spybot didn't see it. The anti-virus didn't see it. The virus had blinded the anti-virus program enough that it ignored it. The virus had also hidden the links on various web pages that allowed online virus scanning, or generated script errors or even where you can download a new antivirus program the buttons were gone.
I knew something was there, but the only way I found which one it was, was to download AVG trial to another computer, use my thumb drive to copy it to the infected computer, reboot in safe mode and install AVG, then run it. Note: AVG Free didn't find the virus and in fact would go disabled while attempting to scan for it. It took downloading the full version, even if it was a trial, to snag the little critter.
Once the virus had been quarantined and the mess cleaned up (use ccleaner multiple times for this), there were some DLL files that I had to re-register in order to repair the damage that it did. After that was done, the script errors, web page links and most of the other symptoms disappeared. However, the user account screens were still corrupt (couldn't do anything) and his profile had a few other problems that I couldn't repair, so I created a new user account and copy his files to it. Everything worked fine in the new account.