Hi all. A few days ago my system stopped powering on. Specs below.

It would simply do nothing when the power button was pressed. I opened it up and tested the MB power cable in my PSU test unit. Power supply came on, fans came on, voltage showing on test unit. Plugged it back in. Still dead.

Removed parts one by one until it would boot. Removed video card and it booted up to POST beep. Retried, same thing. Tested another video card. Dead. Tested another video card. Dead. Retried original video card. Dead. Retried booting without video card. Nothing?

Right, now it won't power on at all, but when I flick on the power switch on the PSU the motherboard power and reset buttons light up (there are small power and reset buttons right on the MB) but do nothing. I now have it stripped to just MB, PSU, CPU/FAN, still nothing. I'm almost positive it's the MB, but I need to be sure if its that or the CPU before I order replacement. Any ideas would help. Thanks.

SPECS:
Motherboard - Asus P6T
CPU - Intel i7 Quad core
Video - ASUS EAH4870 DK/HTDI/1GD5 (ATI Radeon HD 4870 with Dark Knight Cooler)
RAM - 8 GB DDR3

I agree based on your description it is probably the motherboard. Even if the power supply is out of spec (can you measure the voltages?), the system will hiccup when the power button is pushed if the motherboard is powering on the power supply properly. CPU failures are rare, and boards are usually less expensive than CPUs. Plus, putting a good CPU in a possibly bad board may risk the CPU. But, before writing the board off, try it with minimum memory isolating each module(s) in turn. Also, do you see any vented (top is split, innards may be oozing) or bulging capacitors on the board?

Try remove all cables and cards except on Ram stick.

Connect only the power supply's two cables to the board. Power on.
If nothing try another stick of Ram.
If nothing a stick of ram and a grphics card.

Still nothing, it probably the mainboard but can also be the power supply or CPU.
But probably the mainboard.

Ask a local IT company to check it before you spend money on ordering an expensive part just to find it is not that..



Hope this helps
Grant - South Africa

Power supply most likely. There is a function of all power supplies that self test for good power. If it fails for any reason it will not supply the board to prevent damage. I recently had a similar issue and the supply tested good on all leads for power with a volt ohm meter but still would not power on. I opened it up and found several swollen capacitors. After replacing them with ones from another older one it worked again. Its very difficult to do and a bit dangerous since some of the larger caps can hold high voltage. Buying a replacement is the safest bet. It wouldn't hurt to look inside. If you see caps that leaked or have swollen tops, you at least know it's the supply.