ASUS P7H55D-M EVO
500 Watt Power Suppy (from case)
Intel Core i5-660 Clarkdale
Built new system. Turned on and power would come on momentarily then shutdown. Power Cycles about every 8 secs. Tried another power supply. No Joy.
Now motherboard on breadboard. Only Cpu and Intel retail Heatsink and fan installed. CMOS cleared. New thin layer of thermal past applied HSF seating confirmed. 24 pin and 4 pin power plugged in and power switch plugged in (no other connections or components installed).
Same results. Turned on and power would come on momentarily then shutdown. Power Cycles about every 8 secs. If I unplug the 4 pin (12v) power connector Motherboard comes on and CPU fan turns continuously.
Is the next troubleshooting step to replace the mother board or the CPU?
There are a ton of troubleshooting steps you should take before randomly replacing your motherboard and CPU. There's a whole checklist of items to perform before replacing parts listed in the READ before posting about boot/no video problems! sticky at the top of the forum. Perform EVERY step in the checklist and let us know how it goes.
This started as a new system with the mother board in the case and all components connected (using the clarksdale I5 660 video, WD caviar black 640 b drive, Kingston KVR1333D3N9K2/4G,Samsung SH-S243N/BEBE) . Then I tried simplify components.
I ordered a second case to get a different power supply. When it still had a power loop I then tried all the items in the READ before posting about boot/no video problems. As a breadboard system with just the CPU, both power connections , Power switch and speaker connected , 1 stick (and no stick of ram) this problem still occurs.
The behavior of power loop has been consistent all along. I looked one more time at the the breadboard setup and I will note though the three seconds I reported was how long the retail HSF fan was spinning. Based on observing the power supply illuminated fan the actual duration on may actually may be just momentary.
I would like suggestions on what to try next. Since this occurred in a simplified breadboard setup I presumed this pointed to a motherboard or CPU issue. I was hoping to figure out if it was time to try a different motherboard or CPU an if so which one?
I am not a newbie builder I have building systems for at least 12 + years, but I usually only build a system or two a year so I am sure there is a lot for me to learn that I don't know.
Are you sure your HSF is seated correctly? It should not move if you try to wiggle it. Check that you can see the plastic posts sticking out the back of the motherboard slightly, and the pegs fully pushed through those.
Thanks for the suggestion. Though while it was bradboarded all the pegs were properly poked through.
Asus tech support answer given what I had tried they suggested mother board. I rma'd the board received the new one yesterday. After reassembling the same the new board the computer booted properly the first time. So it turned out to have been the mother board.