PC will not POST. Help required!

[R.C.Anderson]

I've just taken my PC apart to replace the watercooling coolant & pipes, cleaning out the blocks whilst I was at it. Obviously this means almost completely dismantling the PC (something I've done on numerous occasions previously, so had no concerns about).
Unfortunately once I had reassembled everything & hit the power button to turn it on, nothing happened...
When I say nothing happened, I mean nothing, the fans didn't even move.

I've got an LED on my motherboard which lights when there's power (even is standby), which continues to be lit.
I've tried disconnecting the PSU Mobo connector & manually turning the PSU on, and it turns on & spins the fans & my pump correctly.
I've tried bridging the 2 mobo PWR SW pins manually, nothing happens.

Does anyone have any ideas as to what might be the issue, or any ideas for troubleshooting?

Specs:
Mobo: Asus P8P67 Pro
CPU: Intel 2500k
PSU: Corsair HX750W
GPU: 2x ATI 7970s
RAM: 4x 4GB Crucial Ballistix

 

[The Artfull Bodger]

Gpu seated properly and power cables?

 

[Plec]

Have you tried some of the other staples yet:

• Clear CMOS
• 1 stick - rotating sticks and slots
• Reseating all cables/connections
• Warping of the board around DIMMS/socket
• Motherboard secured
• etc...

 

[R.C.Anderson]

Gpu seated properly and power cables?

Checked all that, and seems to all be connected properly.

Have you tried some of the other staples yet:

• Clear CMOS
• 1 stick - rotating sticks and slots
• Reseating all cables/connections
• Warping of the board around DIMMS/socket
• Motherboard secured
• etc...

I've tried reseating all the cables etc, but I haven't tried with different RAM sticks (as they never came out of the mobo), or clearing the CMOS yet.
Everything seems to be secured properly.

I'm going to try clearing the CMOS, and trying with only 1 stick of RAM this evening.

 

[R.C.Anderson]

Managed to get it sorted last night

Tried unplugging everything that's not required to boot, down to 1 stick of ram (tried in a few different slots), still nothing.
Tried using a PSU from my media PC, still nothing.
Drained my WC loop, and removed both GPUs, it booted.
Placed 1 GPU in, it booted.
Swaped the GPU for the other one, it did nothing.
Removed the waterblock from the GPU that was failing, and retried, it booted.
Placed the waterblock back on, and retried, it did nothing.
Took 1/4 turn off each of the screws holding the block on, and it booted again.

Although I couldn't see anything, I am assuming that either the backplate, or waterblock was shorting out when tightened up.

At least it's all sorted now, although I was getting close to using it as an excuse to upgrade

 

[Plec]

Took 1/4 turn off each of the screws holding the block on, and it booted again.

Glad to read you got it sorted.

That was a nice spot/experienced test.

Show's how close the tolerances are - and how expensive they can potentially prove too.

Shame about your excuse for a new build - perhaps a re-tighten in 6 months...

 

[R.C.Anderson]

Glad to read you got it sorted.

That was a nice spot/experienced test.

Show's how close the tolerances are - and how expensive they can potentially prove too.

Shame about your excuse for a new build - perhaps a re-tighten in 6 months...

Yea, I was rather surprised at what it was, as I was kinda resigned to thinking I'd broken something along the line (so much so, I'd actually pulled out my contents insurance paperwork to see if it would be covered under the accidental damage cover I have!).

Like I said, I couldn't see any evidence of anything shorting, but I can't think of another explanation for it!

The other half wasn't so impressed when I said how close I was to upgrading but as I rarely use it to capacity nowadays, the sensible side of me knows I'm right not to!