No PC power up - black screen

[night flyer]

Hello,

my PC worked fine for 2 months on air cooling, 3 days ago I installed a water cooling sys, everything was fine until this morning: power cable connected, before hitting the On pushbutton I could see the Dram red light blinking on the mobo. I kept the Memok! button pushed for a few seconds for syncronization and the PC started on its own (which is very weird) but I did get just a black screen, nothing else. HDD was writing for a couple of seconds at power up but nothing thereafter. I tried to run the mobo without DVD, hard disk and RAM, still nothing on the screen. I also tried to reset the BIOS with the relevant jumper and to remove the battery: nothing at all!
System is as follow:

Asus M4A89GTD PRO/USB 3
AMD Phenom II x6 1100T
DDR3-1600 2x4 GB Corsair XMS3
PSU 750W
Radeon HD6870
HD Seagate 3,5"2TB Sata3

Most likely mobo is dead, even though the green led is always on and fans are spinning as well as the water pump. As it could also be a CPU or a RAM problem, do you know if there's any way to see which part/s is/are dead? I don't want to buy a new mobo to find out that the problem was in something else.

Thanks!

 

[sadams04]

Would doubt it is a CPU or PSU problem. I would start with trying different memory since it is cheap. ...and double check all connections to the MB.