Dell E6500 held sometimes during working

Hi,
Dears,
I have a problem with my Dell E6500. Sometimes during working it held, so I turned it off forcefully by on/off button. after it, when I try to turn it on, it turn on (just lights on, does not show display) and then turned off.
I consult with a frined. he tell me a way. "eject off its RAM, Battery and cell (storing time)ejector from motherboard and leave it as it for 2 hours. then put RAM, CELL and battery and try to on."

I have done it, it starts and worked fine for 15 days, then again I face same problem, I again repear the process, it turned on again but now I failed to start it on.

what problem it really have, Any suggesstion advice Plzzzzzzzzzzzz.
waiting............