laptop shutting down before/after boot up

I have an hp dv5-1002nr laptop which continues to shut off sometimes at random times. Sometimes in windows when i run more intensive programs or just install a program it will shutdown. Other times i press the power button and it shuts down 2 seconds later and for a long time i cant get passed that point. This is a list of what ive checked thus far.

my gpu- i disabled it and it still was having problems shutting down.
HD- Removed it and shut off before i could even get to the screen to tell me there is no hd installed.
RAM- Reseated and tried booting up w/o them,still shut off in a few seconds.
PS - tried using a different power supply( even with one with more watts) still shut down.

My laptop is now out of warranty so i took the whole thing apart to check on overheating issues. Got down to the heatsink and fan. The heatsink was not cracked or bent and the fan runs like its supposed to. Then i took the heatsink off to look at the thermal pads laptops come with. A few pads covering other parts were intact but the one over the processor was not. It was kind of melted around the processor chip and a little bit was left on the heatsink. So i cleaned it up and used new thermal paste. I put the laptop together again and got lucky enough to get into windows this time and run cpuid hwmonitor which showed me the temp on the cores were around 57C. Ran some other apps and it shut down again at only 62-63C. The laptop was not hot on the bottom and the laptop sits on a cooling pad. I believe i didnt use too much paste (about half a bb) and the heatsink is properly on and its tight. Maybe something on the mother board blew out earlier? Maybe the temperature sensor is incorrectly shutting my computer down? So if anyone has any ideas what the problem could be now i would appreciate it.