is this the mobo.......or what?!?!?!?!?!

I am trying the fix my grandma's comp and i can not figure out what the problem is, first here is the specs:
Chaintech VNF4/Ultra
athlon 64 3500+
2x1g PQI turbo
250 western digital hd, 80gig Western Digital
6600GT
light-on DVD, Light-On cdrw
Thermaltake X Case (Black w/fan controller)
POWMAX Demon power supply

Heres whats happening first the computer was running real slow and had various error messages from a bad ass virus that was hidden in a pixel in a picture that she opened in an email. So i Erased XP and reinstalled it after not being able to go into safe mode or anything else, however it took over 24 hours to install and i knew from the get go there was something wrong. Finished installation and mobo drivers which took another 10+ hours of installation. Processor is running at 100% constantly so it can't be the ribbon cables as told to me by a tech from bestcomputer usa. Or the xp cd which i have switched out now after 5 times of retrying. After that I thought mabye it was the HD so i tryed them both in another computer and tryed booting windows on the 250 instead of the 80. The same problem occured again and both hd's seem to be fine. Reinstalled windows again took another 24+ and restarted comp and blank screen appeared now i thought it was the ram. Took out the ram put it in another similar comp which is running AOE 2 right now and working fine. I took the ram out of that comp and put it in this one and i thought i had fixed the computer because the screen started displaying and i was reinstalling xp rather quickly and at this time i left for the gym, when returning an hour later a blue screen pops up. It says something like windows xp will not lode so your computer will not be permanently dammaged, turn off shadowing or cache in the bios or something about fixing the hardware and bad ram. I tried restarting the comp again so i can see exactly what it says however nothing will appear on the screen again. Thinking about flashing bios however ive never done it before and i have build 6 very good computers and 4 of which can run any game out great.

Well thanks in advance for the help........any comments appreciated!!!!!!!

Hold on, could you clarify the HD situation? My comprehension sucks, so are the hard drives bootable or NOT? Did you do a LOW LEVEL FORMAT, or a quick format (from Windows Disk)? If you didn't do a low level format, then the virus could still be on the HD.

that's your GRANDMA'S computer? it's better than mine is, that's for sure...