Computer emergency shutdown?

[Deto]

Little history, I got 2ghz AMD Athlon XP (2800+) with 1Gb ram, with Radeon 9600. I also sport basics, two harddisks, DVD drive, 17" screen (I think ), crappy ViewSonic keyboard and mouse (with wonder button named as 'Close' which crashes any program available to windows) and USB hub with printer, B4 (slightly bigger than A4) wacom tablet, memory card reader. Mouse of course goes to USB too. The power source says max 300W and Voltage 115/230 (no idea what that really means )

And what happens from time to time, is my computer hard cutting power off and 'Beeping' sound coming from either Motherboard or Powersource, it ends only if I pull the powercord out. I've tried to find the problem, forums such, but only thing I can find out is that it's probably motherboard alarm, that's pretty much all.. Not even the AMD/Athlon page had anything helpful about it. I myself suspect its the CPS (Computer power source, whichever the real word is) giving either 'kicking power' or giving too little :P

When it happens, I can run my computer forever non-stop (always on), but I got alot of those 'shut downs' with X2 (very graphic heavy space simulator), I have those with some other things too, I got no problem with Max 4.2 which I use, but when I tried rendering old scene in Max 8.0 demo (unlicenced version), the same thing happened, midway through :P

Its not 'computer forces to shut down' like normally shutting down comp, it literally kills the power, it doesn't give me warning, suggestion, it doesn't carefully force computer off... it commits a machicular suicide...

EDIT:

Motherboard monitor says the changes to the CPU power / such voltage ain't too big, they stay pretty much average with high and low. Heat is from 44 to 66 celsius at max. The BIOS alert should be ~74 or so

[Deto]

Thanks Rinne, I must test around in Bios to see if it helps, I'm not sure though when I get any results, cause it don't happen that much

I also checked the calculator, I forgot to add external network card and internal one too, ending up to ~280-285W need. Oke, HAHA, I also have my old CDRW plugged in... so add more to the W needs...

However, hmm... I'm a bit afraid of lowering voltage on cpu and memory, what kind of effects it has? I mean, I've heard that lowvoltage can cause serious issues

How can I identify what I have as cooling paste / pad and or how to deal with it? I've done lots of changes to my comp, but never that. My dad always did it (He didn't really trust me on that)

Maybe I should remove some things from comp, such as the extra CD drive (Which don't even work, I don't know why I still it, I remember unplugging it, duh) and the network card,I installed it because I had tons of problems with my internet con, but in the end it turned out the ISP had blown their router server up

Hmm I don't quite understand the how the counting works? First I got way over 16000 before I stopped counting, then I got over 380...

Thanks again

EDIT: I reseted MBM yesterday (Motherboard monitor) to get clean data, computer ran overnight 'idle', the heat rised to +65 celsius at peak :P

Haven't yet removed 'insides', still checking

EDIT2: Average is 54 temp, current 48, near idle, only ircing and writing here :P