Anti-virus software is great when it's working, but can be a real pain if it stops! I recommend AVG 7 Free version, but then I am a techie who likes to get stuff for free! It has less features than some of the competition, but I've found it pretty good and have installed it on many friend's PCs.
Often if you get a problem like yours, the only way to solve it (unless you want to spend hours on the phone to McAfee with no guarantee of a fix at the end) is to uninstall or system restore to a known good point. I don't think there's any magic wand software that will automatically go in and fix your problem for you. Sorry!