I don't recognize anything specific about your problem, but in many cases of computer slowdown you are likely to find an accumulation of temp (temporary) files on the machine.
Assuming that you are using some version of Windows(?) you can get some cleanup by going through the routine:
Start - Programs - Accessories - System Tools - Disk Cleanup.
The Disk Cleanup routine should show you how much disk space is being used by temp files and temporary Internet files. It is generally safe to OK and delete them all. This routine should not delete "cookies," so you have to handle them separately.
I don't know if this will help with your McAfee blip. An email to them is probably your best bet there. But it might help clear some of the slowdown.