I would check:
-Is your heatsink/CPU fan sit properly , (thinking to overheating, cooling paste problems etc...)?
-Leave only one Ram stick and try to boot
-Is your MB, Processor and GC properly powered?
-Check for any short between the MB and the case.
(Remove the MB from the case and start it outside)
-Did you have any trouble installing the processor?
-Try to reset CMOS.
It's all what I see for now.
Check the error code (Q-code) on the mobo. It may well be that the installed memory is not properly recognized by the BIOS and causes the system to hang. You have to flash the BIOS asap, but to get past the Q-code error, you may have to remove some memory sticks first.
I had this (or at least something very similar) happen once and the issue was that I forgot to connect the second power port on the motherboard. This is the 8-pin connector that is usually but not always on the CPU/Memory side of the motherboard. The Q-code display wouldn't even light until this connector was filled.
I agree with Kouper's 1st comment... check your heatsink/fan
2 or 3 computers ago I built a computer where one of the 4 cpu heatsink/fan legs was not "tight" and the computer would not start because the CPU would "immediately" trip the built-in heat sensor and send a signal to the power supply to shut down
It may be the reset swich. Unplug all of the front panel cables and just leave the power cable connected. I have sometimes used a screw driver to jump the power on. My P9X79 WS board has an on/off switch onboard.
Also check cpu power connector / power supply.
Thanks guys, re seated the RAM and a couple of other little things. I should have quit once I got tired. In the morning she fired right up.