|I'm going to assume that you don't get any beeps as you didn't mention anything like that. A few suggestions comes to mind:|
1) Try booting with another monitor to make sure the problem is not just in your display (though it's unlikely it's easy to test if you have the monitor)
2) BIOS rescue disk or CMOS-jumper or -battery reset. In case your BIOS is corrupted for some reason. (Search online for instructions)
3) The last resort: Take out all devices that you don't need to get the computer running (Leave only: Mobo, CPU, PSU). If this works and you get a POST beep(s) then you can pretty much rule out Mobo, CPU and PSU. Then just add a one at a time the parts you removed. (Start with memory and GPU) You should be able to identify the culprit this way.
I hope this helps.