My guess is your hard drive is going bad. For all brands and models except Toshiba drives, you can go to the manufacturer's web site and download their drive fitness tests to quickly learn if it is going bad or has other problems. Also look at the S.M.A.R.T results.
I am a bit dumb so I don't know what 12b sd ram is, but you need more ram to run W2K well with SP4. The continual updates provide so much bloat that the system cannot survive it.
And finally, you might want to take another look at your security by runnning an outside scan for infestations such as Virus, Spyware, and the like... Being aware that a lot of the antivirus and Antispyware companies no longer support Windows 2000. Try, also, Spybot and Adaware 2007.
Then download and run HiJack This latest version and see what is reported there.