No display problem

Hi,
I have dell inspiron 15 series. But when i press my power button, my laptop doesn't start. The power indicator LED get start and no display. This started 2 months ago....i tried all your solution but nothing worked( press the power button 30 sec, 5 sec) and i dont think that its a motherboard problem cuz my laptop start sometimes. One day i tried alt+ctrl+delete and it worked but when i tried again, failed.
What do i do.....plz help