What operating system and service pack, if applicable, is this and are you totally up to date including parts you may not use such as Internet Explorer?
Have you been running any registry cleaners lately, if so can they restore whatever they took away?
Have you experienced any hints that malware may be present?
Try running the Virtual Technician as it may be able to fix things http://mvt.mcafee.com/
Got to Start/Run or click the Windows key + R simultaneously and type in services.msc and click OK
OK any prompts and in the list scroll down to Windows Firewall Service and check if it is Starte dand Automatic.
If it isn't double-click it and edit it to make it so, if possible.
If it isn't there, Technical Support have a fix and they are available via phone or online chat under Useful Links at the top of the page.
Insist on them escalating the case if they dither or suggest it may be a virus.