A friend of mine was having similar problems with McAfee. Try to disable every refrence to it in Startup and use Ctrl-Alt-Delete to make sure there is no McAfee stuff running, then uninstall it.
Then dump it.
I tried for ages to get it running for them as they had already paid for it, but after spending most of the evening on it they decided to try to get their money back. They are now happily surfing with AVG and Zonealarm.