|I thought your problem sounded familiar:|
Why did you not respond back on that previous thread?
Since it worked for awhile after you opened it up it may be a bad connection somewhere. I had a somewhat similar problem when the ATX power connection--the one with 2 yellow and 2 black wires--wasn't connecting good.
Between the Motherboard or power supply it could be either or both. Sometimes a failing power supply will ruin the motherboard.
If you think it might be just a motherboard problem take a look at the capacitors, especially the ones around the cpu. Do any of them look puffy, like they're about ready to blow up? If so they're failing. They will soon be so far off specifications that the motherboard will no longer work.
If it's just the PSU the best thing is to just swap in a known, working, compatible PSU and see if the computer works right.
Maybe the problem is with the drives or add-on cards (if any). Try temporarily disconnecting all the drives and remove all the cards and see if you get the normal posting screen when you start it up. If so the problem is likely with one of the removed items.
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