Why wont my tabet turn on?

My Galaxy tab 2 wont turn on. It has done this before and if I took the back casing off and put it back on it corrected the problem. Now it doesn't turn on no matter what I try. I have tried all the different button combinations I found on the internet. Still nothing. I have replaced the battery. It charges fine. I took it to a corner store repair shop and was told that there isn't any power reaching the motherboard and should just buy a new one. It was a gift and I want to repair it myself if I can. Can anyone help me?