Dell inspiron 5110 screen black out

When i switched On my dell 5110 i could see the system working. there was a slight indication on screen that it was on as the color turns from all black to light black.CPU run fine but the screen didn't come.

I connected the system to external monitor and it worked fine.i was thinking that the screen was defective but when i took it to service station, and switched it on it worked fine 3-5 times.

when i checked it again for longer duration it worked fine and then suddenly the screen went dead again and system in sleep mode. i switched it off and then the same problem appeared and screen was not working.

few hours later it worked again. and now it is unpredictable. it works sometimes and sometimes doesnt.

i have taken it to service centre couple of times but the same thing is happening. we have checked connections and they are fine too. the service guy is saying it could be faulty RAM and suggesting me to get a new ram.

i believe display is fine because it works many times. plz suggest should i get a new ram or the problem is somewhere else.