laptop wont start.

i have this laptop that will not turn on, well on occasion it will turn on for some reason, but it dosent stay on for more then 30 seconds. i took it to a shop and they said there was a problem with the motherboard, and that it was broken, but i don’t think so because it still turns on. the one thing that i can think of is that maybe the place where i plug the charger is broken or something.

thanks in advanced for your help.