I'm going with "another clone PC" so you may want to consider how much you are willing to invest. Without seeing it I'd go for a new power supply. Increase the size to about 600+ Watts so if we have to replace the motherboard and other parts we don't have to replace those.
Bob
ITS BEEN about a week now since my desktop 'died'. I removed one stick of ram to see if the ram was the cause..but the post for the short time it worked, acknowledged it. ..also my dvd, hd;s ( 2 ). Now each time i try to get into the bios, I am getting to see less. I'm trying now by process of elimination, removed power from HD's,dvd, and even my video card. The latter surprised me..by removing the v. c. how can I tell what may be causing the problem. Now, at this stage, i turn on the pc and there are no beeps and of course there is nothing shown on the monitor. All fans are working, and then after about 30 seconds running, it shuts itself off.
XP-SP3 ABS desktop

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