PC was freezing/hanging, now limping on last leg

This is long because I tried to add as many details as possible. About 3 weeks ago I caught a virus(es) on my pc and started clean up with malwares bytes and online scanners. I had vundo, but wasn't getting the usual spam popups that seem to be the usual indicator. Actually nothing really unusual on my pc. I got it all cleaned up I think pretty thoroughly (MAMB, ad-aware, spybot, running in safe modes, my own mcafee which seems to never find anything, etc..). Eventually all kinds of virus scans show nothing, assumed clean, computer fine.

So now about 2 weeks ago I encounter a new problem that is this hanging/freezing while playing media of any kind. Online, dvd's, etc.. Again thought I had a virus, began clean up and combing through my pc, but I couldn't find anything malware related. During the media playback it would start to repeat/skip, slow down real fast, then stop (about 4 seconds from noticing problem to freeze). Now about a week ago the problem migrated to freezes while doing nothing, but usually initiated from clicking an option, x-ing out a window, starting a program, etc..

Now today it went to the next level. I downloaded a memory diagnostic file from microsoft, [oca.microsoft . com/en/windiag.asp] (I've been suspecting my memory). I tried to download the file to my desktop, but strangely mozilla kept crashing out. I tried to open IE and it would just instantly crash. I shut it all down, started it up and tried again. Same thing. So I downloaded the file on my other computer and burned the .iso file onto a cd. Now with the disc I tried to get into my BIOS to change the boot location, but the opening BIOS screen would not respond to the <del> or <tab> at all. I called Asus customer service and sure enough it was not responding; different keyboards, usb ports and PS/2 ports. So he had me switch out a jumper pin of sorts on the board that resets/configures BIOS. That did it and I got into BIOS setup. I had changed the boot location to only my cd/disc drive, but it will not boot the disc and keeps giving a repeat message put boot device in or something. This is still a problem.

Also, yesterday I popped out one of my 1GB ram modules. Microsoft says I have changed my hardware configuration and tells me I have to re-register in 3 days? What the hell is up with that??? Well I did. So today, after the boot disc problem mentioned above, microsoft is demanding I register my windows even though it said I had 3 days (actually I swapped out the memory a couple times). Finally, when I try to register online it just logs off and repeats, it is not connecting to the internet or something. I'm gonna get the activation code tomorrow over the phone to bypass the online registration, hopefully get back to the desktop.

I built this computer about 2 years ago with:

Intel E6750
evga 8800 GTS graphics card
520w corsair PSU (plenty of amps)
2x1GB corsair memory
asus P5K board
westgate HDD

I play a lot of games, WoW, CoD4, etc.., never had a problem except occasional virus. Even when the thing was freezing from media I had never had problems when gaming. This is beyond my pc skills, I hope someone here can offer up suggestions. Am I dealing with multiple problems? Virus? Hardware failure? I've never had a problem this bad before. Please help!!! My computer is my livelihood and this is slowy driving me insane...

BleepingComputer.com: PC was freezing/hanging, now limping on last leg