Spyware, viruses, & security forum: McAfee not working--could be virus, or just hosed?

[Sorry for the double-post...I originally put this in 'Computer Help' but afterwards thought this was a better place for it!]

First, a few specs: I have an eMachine T3418, running XP, which I've had since mid-2006. I'm updated on all the drivers/add-ons/service pacakges, etc, as far as I know.

This is by far the strangest problem I've had on my PC...especially since this happened AFTER I did my weekly run of McAfee/RegCure/CCleaner/Ad-Aware, et al. The only websites I went to after running them are Amazon, Yahoo, Live Journal, and Facebook. I ran all of these cleaners and scanners this past Saturday and no issues came up, but turning on the PC on Sunday morning this all started.

McAfee is not running, I can't update it, and I can't reach their website (I keep getting 501 or a 504 error). That is, I can *start* it, but can't get any updates and it stays in "initializing" status if I run it. I can, however, reach other security sites such as Norton/Symantec, Ad-Aware, and so on, without any problem. I've run all sorts of virus checking software since then and they're not finding anything. I've run CCleaner, RegCure, and I'm currently running Ad-Aware as we speak. I've also run a few programs I downloaded via a different computer to check for Conficker, but they're not finding anything either.

I should also add that I have no problems going to any other websites (not to worry, I'm only going to ones I know are safe), though both my browsers (IE8 and Firefox) can be a bit slow, and my system has been having a few hung app crashes lately as well, even before this issue came up--not many, but enough to be annoying.

Any ideas/suggestions? Would doing a system restore or even reinstalling the OS help? And are there any downloads/threads here that I might have missed that I can try?

Thanks ahead of time!!