Trying to figure out dead computer

It's been sitting for a year and now I have some money for parts, I'm just trying to figure out what I might need to replace.

Over the years I had had to clean up a few infections on it. After one incident I had removed the virus, etc but the performance was spotty. I wiped and reinstalled windows but the fix was temporary and it continued to deteriorate, It stopped recognizing the cd/dvd rom in the bios (and I had no floppy drive to boot from thanks to the genius who built it) and I couldn't get the windows disc to run to try another reinstall or fix. I once managed to get it going with Hiren's Boot disk and I managed to rescue some files then it stopped recognizing that disk completely as well.

Finally, one day when trying to boot it up all it would do was make a beeping noise like it's alarm sound. I can't even get to the Bios screens now at start up.

I'm not completely sure of the particulars but it has
An Asus 939 socket motherboard with an athlon II 64-dual core (I know, obsolete,but it will be cheap to replace if needed)
A Invidia Gee-force 7600 (?) card (which works fine, I've put it in another machine to test and it's OK)
Running windows XP pro

Any ideas?

 

Maybe a flat battery in the BIOS seeing as how it doesn't post!

 

And/or a failing PSU.