Go through the following malware removal steps systematically, doing
everything with updated tools in Safe Mode. You may need to get the
programs and updates from a different, known-clean computer with an
Internet connection and a cd burner (or have a usb thumbdrive with
enough capacity to transfer the files).
You will note that the removal steps start by scanning with an
antivirus. If you do not have a full-featured current av installed (not
earlier than 2004 and using updated definitions), then start your work
with TrendMicro's Sysclean. The instructions for that are at the same
link.