You could try to run the McAfee Virtual Technician found at the top of this page under Useful Links in the Technical Support area. MVT will scan your computer for any McAfee related issues and will attempt to fix any it may find.
I would suggest you review the information in this documentRequired Reading - Home User Assistance Malware Troubleshooting to narrow down what might be the reason for the change. Please run the Stinger scan mentioned in the link. Run a McAfee full scan and make sure you are up to date with Windows.
After following the suggestions in the document if nothing found try running free version of this programhttp://www.malwarebytes.org/mbam.php and see if it finds anything.
Keep us posted