Faulty RAM is also a common cause of your type of symptoms.
That's why people keep asking about the 8-pin CPU power connector and if you've tried with one stick of RAM.
A computer powering on but not displaying video output is very common and the reason the sticky linked above was created. The chances are very good that if you actually perform every step in the checklist you'll find your problem.
Ok I have the same problem, they tell me to hear the beeps, there no beeps, i change the video cards, and nothing hapens, I need more help. I have the same configuration. please tell me what works for you