Dell laptop screen not turning on

Hello,
When i switched On my dell 5110 i can see the system working. there is a slight indication on screen that it is on as the color turns from all black to light black.CPU runs fine but the screen doesnt come.

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

i was at home first 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 took 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.i have checked connections too they are all fine. plz suggest should i get a new ram or the problem is somewhere else.