oky well the best troubleshoot you could do is that.
1. Take everything apparts.. remove the mother board from the case.
2. Put the mother board on a safe spot.. like on some wood surface or on a antstatic bag.
3. Plug only the power, cpu, ram and the pc speaker, try to start it up ( you can short the 2 pins where u plug the power switch with a small screw driver )
4. NORMALY it should beep to tell you that the video card is absent. (unless you have one onboard )
5. Plug your graphic card and your monitor.. start it up.
If it doesn't start at that point.. there's a serious problem...
Check jumper / dip switch IF you have any one it...
make sure the CMOS reset jumper is on the right position.. in case it would be in "reset" position that would be your problem ;)
6. If it starts, add ONE after the other each of you peripheral...
you should find the problem that way..
hope it helped you
wolfien-