Question Motherboard "powered" but doesn't turn on

[F4BIOD3V]

Hi there,

I have an old computer that is still worth using and I have a problem which I'm not able to resolve:
The motherboard get powered by the PSU but when I press the power on switch, it doesn't turn on (no fans are spinning, no POST, neither beeps..) just like I didn't press the switch.

The motherboard is a new one.. I have replaced another one (that shown the same problem) some weeks ago.
The PSU is a Corsair AX750 and I have tried also using another PSU but the problem is still there.

In your opinion which kind of stuffs should I do in order to solve this problem?

I have done some tests and these are some details I can tell you:

• When the system is started, the whole PC works great! It doesn't shut down by itself, it's quick while doing tasks and even cool (never reached more than 80°C even on heavy tasks).
• If the computer doesn't turn on, removing the PSU wall cable and reinserting it, helps in turning it on.
• I also tried inverting the switch (reset/power) in order to know if the switch was faulty. Obv. it wasn't.

===== FULL SYSTEM SPEC ======

CPU: i7 860
CPU COOLER: CM Hyper 212 evo
MOBO: H57H-AM2 (new) -> P7P55D Le (old)
PSU: Corsair AX750
RAM: 4x4GB Kingston DDR3 1333Mhz
GPU: ATI HD5770
HDD: WD 1TB
ADDITIONAL: 1x DVD-ROM + 1x CARD READER
CASE: CM 690

 

[rgd1101]

full system spec? include make and model of the psu