Before i fully assembled my computer (to the case), I did a pre-test with the whole system, It turned on just fine but I only could have turned it off using the PSU switch (clue?), not the power button, when I fully assembled it, the light from the mother board was the only thing working. What could have happened?
-ASUS P5G41T-M LX PLUS - LGA 775 - G41
-Cooler Master RR-910-HTX3-G1 130-Watt 92mm Hyper TX3 CPU Cooler
- 4gb DDR3
-Cooler Master Elite 460W ATX
-ASUS EAH6670/DIS/1GD5 Radeon HD 6670 GDDR5 1 GB
- 3ghz Core 2 Duo CPU
More about :upgraded mobo graphics card system work
I'm guessing your CPU cooler is installed incorrectly. I had that same problem when I upgraded my system and I reinstalled the cooler exactly how the instructions had it and it works perfectly fine now.