No display

Hello,

I have a problem with my cpu. No display when powered on. the led light which indicate booting blinks about 3 seconds only then stops, power on led light is the one left lighting. I used to replace the ram and everything will be working continuously. It will turn off properly. But each time I turn it on, no display again and the booting led light stops for 3 seconds. I Have to replace again the ram so that it will run again. It is always the routine, again and again. What seems to be the problem in it? Both the ram which I always used to interchange is working in other cpus.