Boots sometime, after its off it doesn't start

I purchase this laptop and it was working fine for about a day, it came with Windows 7 64bit so I installed Window 8. Then it was running fine and automatically shut off. I tried to turn it back on but it wouldn't turn on. I have taken it apart cleaned the fan and added new arctic silver 5 to the CPU. It runs of of the AMD C-50 duel core clocked at 1ghz not the best processor but it runs. Please help because it's off and I can't turn it on.