Laptop dell ispiron 8600 dead?

Hello,this is my first question on this forum and i hope i will get the right answer.
I have a dell ispiron 8600 witch would not start.when i press the start button is switching on and is loading and the dell sign appears on the screen ,then after 5 sec it is switching off without any warnings.
This laptop felt off and after that never start.i tried to change the RAM socket-no result.i tried to start it without hard-no result.i tried to start it without cdrom-no result.
This laptop wasn't mine but now i am trying to fix it for my son.So if anyone knows what i should do please tell me. Thank you in advance.