Recently after being booted up for a short time only up comes "windows is shutting down" , the screen goes black but the powerswitch is still lit up and can not be switched off. After a little while power goes off, after another litlle while power comes back on by itself and keeps trying to boot up again and again and then it shuts down for good.
I switched back on in the morning after and all went well for about 20minutes or so and then it was on again off again and off. Power supply checks out OK, so does Ram. I Booted up with fail safe settings, but no difference.
Any advice would be much appriciated thanks.

Welcome to the forums

First things to check is the temps in bios

If its telling you its about to shut down then it sounds like auto shut down settings in bios maybe set too low or the temps are too high.

What tests did you run on the ram and the psu?

Please list full system specs too

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Opteron 165@ 2970MHz (330x9)
DFI Lanparty Ultra D/ TR Ultra 120/2x1Gb G.Skill @250MHz
BFG 8800GTS (750/2000)

Thanks for reply PostmanFw!
You seem to be on the right track with temperature problems. It has been very hot with very high humidity here in N-Australia.I managed to run PC1 yesterday morning for a while and set the BIOS to "fail safe". Temperatures are now down and I had PC1 running for 2 houres before I loged off to go on PC2. What now? The system did check out OK.
Here are my specs:
Gigabyte socketA motherboard 7VT600 1394
AMD-Athlon XP2600+ with L2 cache of 512 KB
768 of DDR memory
NVIDIA G-Force MX4000 AGP 8x 128 DDR
Windows XP Pro SP2
450 Powersupply
Regards Seaibishors.

What are the temps reading at full load using orthos/prime 95? Use speedfan to measure temps.

Also what vcore is it set at in the bios? Should be 1.65v

Fail safe mode will be setting it to a lower fsb (100 prob) so the chip runs slower. What settings does it load when optimised defaults are loaded? Should be runing at 11.5x166Mhz if it a xp2600 barton core.

-------------------------
Opteron 165@ 2970MHz (330x9)
DFI Lanparty Ultra D/ TR Ultra 120/2x1Gb G.Skill @250MHz
BFG 8800GTS (750/2000)