Power Supply noise

Gateway desktop running Win XPHome
AMD CPu, plenty of memory
Power supply is the one that arrived with
ASTEC model ATX 250-3505 250w

Have recently re-formatted and re-installed op sys due to all these hang probs. Also was not (and will not) boot up first time each time. Just fails and get blank screen. Have to manually shut down and restart sometimes two or three times before boot.

I've had the case open for a while and get my ear in there as much as i can. I am sure it's not the drive that is producing the noise I am describing. But....just now i am listening again and trying to hear if it might be coming from one of the pci cards (network, sound, video) just cannot seem to tell.
i am attempting to defrag the drive and know it's sounds as it works away. It's a different noise i am hearing from somewhere else.

no, no other fans running besides the power supply and the CPU cooling fan.
the video card is a Geforce Mx 440

OK i'm going to do two things;
Re-format completely the HD since I just backed eveything up a couple of days ago, re-install XP and I'll also give a tighter listen to where the noise is coming from. i'll let the forum know the outcome.

Well after spending a day off and on between working at home...i re-formated the HD, re-installed op sys, and the whole problem remains. result is the system just freezes and i have to keep re-starting until i get it to start up. then somewhere in the middle of doing anything, the noise starts up again. It is definitely coming from the top of the case...so i disconnected the Cd drive just to isolate things and sure enough it is coming from the power supply. runs fine for an indeterminate amount of time and then a bit of a soft grinding and the sys. freezes up. tomorrow a new PS is coming for a visit. thanks for all who replied.