So, you have three options left:
1) If you are unsure about computer stuff, so should just take it to service if you have warranty. Or should take it to service and pay for it, if you don't.
2) Clear your CMOS. There is a jumper on your mobo, which is marked like CMSCLR or CLRCMS or smth like this. You should disconnect your computer from power (better physically by unplugging the cord), wait until motherboard led if off, remove onboard battery and move the jumper to another position (e.g. if it is on position 1-2, so move it to position 2-3 for about 20 seconds). Then restore the jumper setting, insert the battery and plug in the cord.
3) Try removing system parts one-by-one:
- Remove discrete video (if you have one) and try to boot. If you receive several beeps, this will mean that onboard video cannot be initialized. This could be because of your BIOS settings or because onboard video controller is brocken. If the cause is in BIOS, you could try clearing CMOS, as discribed in paragraph 2.
- Remove/disconnect all drives, including HDD and CD/DVD and any orther, which you have.
- Remove memory or substitute it to another memory chips, which should be compatible with your mobo. If you have enogh time and don't have spare memory chips, you could try removing current memory chips one-by-one, while relocating remaining memory chip to the first slot of memory bank for ensuring its detection. If you start the system without memory, you probably could get several short beeps, which indicate memory failure.
- You can try removing your CPU, but I'd suggest that if your computer did not give any evidence of life without video, memory and drives, so your mobo should be apparently dead and you should change it and/or the CPU.