Run command doesn't work

I suspect a machine I'm looking at has been infected or hijacked, problem is none of the usual programmes can be made to operate.

Eg. HiJackThis starts up the Warning window then vanishes

similarly the Run command doesn't run anything, it's as if the programme starts (it flashes up) and then closes, this goes for Command, msconfig ect so I can't disable the startup programmes for diagnostic.

I can start in safe mode and login as Administrator and run HiJackThis and msconfig but when I restart in normal mode still no response.

Has anyone come across this before and more importantly HOW DID YOU FIX IT!!!

 

Panic over..............

Lesson number 1

If the PC has anti-virus software on don't assume it's upto date and automatically protecting the system.

I uninstalled Norton and installed AVG7, found over 50 viruses and trojans.

Reboot all OK - well apart from the other problems of course.