Infected?

I've encountered systems that were so badly infected that the OS could not boot up properly. In most cases, I would recommend a full wipe before reinstalling the OS but there may be critical data still resident on that drive. That is where a rescue CD might be useful. F-Secure and Avira are 2 AV vendors that offer free rescue CDs for that purpose.
I tested the F-Secure rescue CD. You basically download their ISO file from their website, burn the ISO into a bootable CD and boot up the infected system from the CD. The bootable Linux OS has a built-in F-Secure AV engine that will prompt you to update its virus detection signatures*. Next, you choose the drive/partition to scan. It will start scanning the selected drive/partition and rename files detected as malware (by adding .virus).

* You need to have Internet connectivity to obtain the latest virus detection signatures.
The high res version of this demo can be downloaded here.