Computer gets power, shuts off, gets power, repeats, never boots

Tews said:

Dont overlook a wonky power supply while you're at it...

I'm comfortable with the power supply. We swapped my PS into another computer and it worked fine; swapped a known good PS into mine and the same problem happened.

Just another update.

New motherboard arrived yesterday. Put it in - and same behavior. And we tried resetting the CMOS on the new and old MB. Have now tried two MB's, permutated each possible way with two PS's, both of which are known to work, and same behavior each time.

Finally for grins (of which I've had few lately), we tried pulling the processor (Intel I3 550) out and firing it up - and the same behavior there. So based on that - the fan cycles on and off about 2-3 seconds a pop, but we never hit the bios screen or anything - plus some googling, we're suspecting it's the processor, which is fortunately covered under warranty.

Stay tuned for more once a new processor arrives.

BTW, other things that were tried and didn't work included disconnecting the restart switch (to eliminate possibility of a short causing this), and doing this all with the MB not mounted in the case, isolated on a piece of cardboard, again just in case some shorting was going on.

I am happy to finally close this thread out.

For the record, what happened was:

• The original processor blew, taking the MB with it (or maybe it was the other way around - no way of me telling)
• Replacement MB did not work (thought MB was the original cause)
• RMA'd the processor, stupidly put new processor in original MB (since thought original MB was good, and wanted to keep as close as possible to original configuration), and that didn't work
• Put new processor in replacement MB and could boot, but system would just shut down to black in minutes
• Blamed memory and replaced that
• Same problems
• Had a computer shop look at things, and after some trial and error, they put a "new new" processor into replacement MB on a system they built, and they could boot to Windows and sustain a session
• So I now have my computer back with the replacement motherboard, the replacement replacement processor, new memory that I had not needed (but 8 gigs now instead of 4) and it's working fine, 24 days after the problem started. Total expenditure was $50 for MB off eBay (dumb, as original was covered under warranty), $50 for two expedited warranty cross-ships of processors, $40 for new memory, and $50 for computer shop to run diagnostics on all my HW. Annoying, but good to be back where I wanted to be.

For the record, although MB and processor are the same brand and rev as the originals, Windows did ask me to activate when I first successfully logged in after putting the pieces together again. I was able to activate in 30 seconds or less using the least-intrusive "Activate online" option.

I'm marking the thread solved. At long last.