Under certain circumstances some people have reported similar issues. There isn't much we can advise you to do except contact Technical Support and have them troubleshoot the issue. It's free by phone or online chat and linked under Useful Links at the top of this page.
By the way I moved this to SecurityCenter for a better audience.
I wouldn't think that it would be necessary to go to all the trouble of reinstalling Windows, but you could try simply uninstalling McAfee, then running the MCPR cleanup tool also listed under Useful Links, reboot and download/reinstall your software from the online account.
Could be that somehow it's become corrupted.
Thanks for the quick reply
Well, I'm at a loss as to what was going on yesterday, as mcshield.exe completely hamstrung my computer, hogging all the CPU (+70%) on 3 out of 4 cores no less.
I did a restart yesterday, thinking it might have got itself messed up, but no dice, it was still hogging all the memory.
However after turning the computer off for the night, all seems to be normal, mcshield.exe is using 00-03% and only 170, 000k bytes of memory.
Minor inconvenience then, but annoying no less.
It has been known for this to happen when the machine is put into hibernation/sleep rather than powering off. That could possibly be the case here perhaps?
It certainly is very odd but I am glad that things seem to be back to normal again.