Here are some things to try:
Run the FakeAlert Stinger
The most commonly reported malware is what we call the Fake Alert. This looks like a valid piece of security software, but is actually malware. Here's an article that can walk you through that. Important notice if you think you have a virus: http://service.mcafee.com/FAQDocument.aspx?id=TS100893
For more information on Rogue software and Fake Alerts: Recognizing and avoiding Rogue Software or FakeAlert Trojans - http://service.mcafee.com/FAQDocument.aspx?id=TS100767
If you're still having problems there are a couple more things to try.
Run diagnostic scanners
Restart your computer and tap F8 repeatedly while booting up. You'll get a boot screen with choices, pick Safe Mode. Your PC will boot in a low resolution state as most processes wont be running.
Go to "My Computer" (XP) or "Computer" (Vista/7) and right-click the hard drive. Select "Scan" from the drop-down menu. All you'll see is an extra taskbar icon which will show a progress report if you hover over it. After the scan completes, make a note of anything it detected.
Run the Stinger you downloaded from step 2 again, but this time set the options to Report Only, and set Artemis to VERY HIGH.
When you post to the community for assistance, please let us know what (if anything) the Safe Mode scan reported, and paste in the report from Artemis.
Not all anti-virus and malware scanners are not 100% within the window between when a threat hits the internet and the security vendor becomes aware of that threat. McAfee uses Artemis technology to narrow that gap, but if we're missing something, we'd like to see a sample of it. It could be a new variant that hasn't been seen yet. If you know which file is infected, please upload a sample using any of the methods described here: http://service.mcafee.com/FAQDocument.aspx?id=TS100095. If we have a DAT for it, the automated system will send you that DAT. If we don't yet, your sample will be assigned to a McAfee Labs Engineer for investigation.
McAfee provides many free tools to assist you at the Virus Information Library: http://vil.nai.com/vil/default.aspx.
In addition to information on thousands of viruses and malware, you can download tools here: http://vil.nai.com/vil/averttools.aspx.
If you would prefer a professional remove the malware from your system, McAfee provides a fee-based Virus Removal Service which can be accessed here: http://service.mcafee.com/SpecializedServiceHome.aspx?lc=1033&sg=VR
Hope this helps,