Hmmm, hate to say this, but it doesn't sound like there's much hope besides a full re-installation. Before you do that though, do what Alan said, get the data off.
Just for future reference, be careful with what you download and install, I would urge you to stay away from any McAfee and Norton antivirus products. Also stay away form some random so called antivirus program show up on you web page, they are untrustworthy, some of them might even be a virus itself!
I highly recommand AVG, it's free, not subscription require, frequent update... what more can you ask for?
Use adaware and spybot to clean up your comp once or twice a week. (Both are free as well). Regclean is another nice piece freeware, use it to clean up the registry once so often. But use Regclean with CARE!, read the instructions first, because it not used properly, it will make some of your programs unusable.
Hope this help.
B.
