What is your operating system and service pack and how much RAM do you have installed?
This issue, if not infection-related, is often caused by McAfee clashing with some other software. Are there any clues in your Event Viewer for instance? Do you have any other software that is protection-related?
Searching the forums brings up many instances of this, the most recent included the discovery that Nero 7 clashed, in particular InCD, and once it was disabled in Startup things improved.
As this is a holiday, help is going to be a bit sparse in the forums I feel so it may behoove you to try Technical Support Chat, free, via the McAfee Support link at the top of this page.
Processor: Intel(R) Core(TM)2 CPU T5200 @ 1.60GHz (2 CPUs)
Memory: 2038MB RAM
Operating System: Windows XP Professional (5.1, Build 2600) Service Pack 3 (2600.xpsp_sp3_gdr.090804-1435)
I do not have nero 7 installed on my computer and no other immediate protection, I have spybot spyware scanner but it is currently turned off. I have done multiple scans and defrags to try and fix it, but even typing this message is proving difficult due to the slow down.
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Try Technical Support Chat then. Your system certainly has enough resources.