In the last 3 weeks I have had more replacement parts than ever before, but I must be missing something obvious. I've built quite a few systems before and had no issues with any of them. Hopefully you good folks can help with this one though...
I originally built a ITX system:
Intel Sandybridge i5-2500K
Corsair LP Vengeance (2 x 4GB) 1600MHz
AsRock Z68M-ITX/HT Mobo
Seasonic S12II-520 520W ATX12V PSU
I had intended this to be mounted in a Lian Li PC-Q11B case...
Working on a breadboard, I connected the up the CPU (with heatsink & fan), RAM and PSU to the Asrock. Briefly shorting the power headers started all fans running and lit a blue LED on the board (no beeps, as this board doesn't have a speaker header, as far as I can see). One second later, all fans powered down with the LED. It tried again, but powered down again and there it looped, unable to keep going for more than 1 second.
I swapped the Seasonic for the PSU on my current PC, which works. I can't recall the model at the moment though, but it is rated at 800W. Same problem. Just to be sure, the Seasonic ran my current PC without problem.
Next I pulled out the RAM, leaving just the CPU (with heatsink & fan) & PSU connected. This time the system didn't power down after 1 second, but I didn't get any beep codes or video output either. With one stick of RAM, back to on/off loop.
I swapped the RAM for some Kingston HyperX (2 x 4GB) 1600MHz, but nothing changed, still on/off loop.
Next I swapped the Mobo for a Zotac H61ITX-A-E. Still the same on/off loop with no beeps (the Zotec does have a speaker header on the mobo).
I have a replacement CPU on the way, but I assumed CPUs are really unlikely to be faulty.
All parts were brand new (except my existing PSU) from Amazon and I reseated everything a few times, just to be sure it was properly mounted.
If you still have issues, tell us where in the list it failed, and we will try to help!
Thanks clarkjd. Notes below from the suggestions in that thread:
2) Yep - the Seasonic has two 4-pin 12v CPU plugs. I've tried both.
3) N/A - The Zotac is currently resting on the bag on a table. The AsRock was in the same place last week.
4) & 5) N/A - I'm using the integrated video.
6) One RAM stick results in the 1 second on then off loop cycle, it doesn't seems to matter which RAM slot on which board or which RAM stick is in it. Same with both the Corsair and the Kingston RAM and the AsRock and Zotac mobo.
7) & 8) Yep - only two RAM slots on these boards.
9) & 10 ) Yep - CPU drops in only one way around.
11) Not that I can see - all looks healthy on the socket and CPU.
12) N/A - using the heatsink & fan that can with the CPU.
13) Yep - CPU fan starts up with the system fan and the PSU fan for every 1 second loop iteration.
15) Nope - the workspace is clear of shorts.
16) Yes - discharged using an earthed case (not on), as recommended.
17) The AsRock didn't have headers for a system speaker (and apparently no LEDs to indicate errors). The Zotec has, but I don't hear anything from it.
18) I'm not using the switch on the case - just shorting the pins for a short time, as suggested in the breadboard threads.
19) Yes - I'm definitely getting power to the board.
20) Yes - as far as I can tell the CPU & mobos are compatible.
21) Yes - reset the CMOS on both boards using the jumper setting. No luck.
22) Both boards offer multiple video outs, just neither stay on long enough to see anything. Without the RAM installed the looping stops, but no signal from either integrated video ports.
23) Everything is snug into the correct sockets, even though the 24pin ATX power cable is a tight fit.
Looking at jsc's suggestions: with just the mobo, CPU & HSF the lights come on and the PSU and CPU fans both work on both boards. I don't hear any beeps from the Zotac (and neither board outputs video of any kind). I've tried two PSUs in this configuration with both boards (both the Seasonic & the other one have successfully power another rig without issue).
Hope this helps. Any suggestions would be welcome!