Pwr delivered to HP Z240, fans work, no POST , no booting, no screen/mouse/keyboard, On/Off fails

[ALR2093]

Power Supply is plugged in and the case power unit is ON(green LED), so is its Fan, the case Fan, and the cpu Fan are all working, loud and fast.   BUT nothing else works. No PowerOnSelfTest events, No lights on the mother board, none on the case, none on on the mouse, none on the keyboard, even the ON/OFF button does not work! If fact you can only turn the "computer" off by unplugging the power cable. Plug the power cable in , and the whole sequence above repeats.

I have re-seated the RAM, replaced the mother board battery, tried to clear the CMOS .

Nothing works except the very loud fans.

Any Ideas about what is broken, Power Supply, Mother Board, CPU. 

Thanks in advanced.

[itsmyname]

A properly-working motherboard should initially run the fans at 100% speed (and noise), and then detect the temperature of the motherboard and the processor. If both components are "cool", the fans will be told to slow down (and get quieter).

A failure for the fans to slow down is an indication that the motherboard has a fatal problem.