Toshiba Satellite L350 Just Turns Off

I am helping someone with a Toshiba Satellite L350 that simply just turns off. It will completely power off when in the middle of tasks. I confirmed that it is not Windows or software related because it would also shut off while running memtest (outside of Windows).

I believed it to be a heat issue (and it still may be) so I completely disassembled the unit and there was quite a bit of dust in the heatsink fan for the CPU and I also replaced the CPU thermal compound with Arctic Silver 5. The temperature of the CPU was down about 8* celcius but after about 10 minutes of running Prime95 it shut off.

Any suggestions or help with further diagnostics to resolve the issue?

 

Set your CPU Temp Monitoring software to log the temps to see what it is when it crashes. I recommend CoreTemp for this.

Just because you replaced the TIM doesn't mean that it actually helped under load or would have solved any overheating issues. This is especially true when using the highly overrated AS5. AS5 takes a good two weeks to cure (break in) and tends to start losing efficiency rather quickly. There are significantly better alternatives to that. Plus in laptops with their proprietary heatsinks it's not at all uncommon for them to not fit properly with AS5 or other liquid type TIM. Many laptops use a tape type TIM that is thicker and fills the larger gaps than a liquid type such as AS5 can fill which causes reduced efficiency under load.

It's also possible that the fan isn't spinning at the proper speed.

And finally make sure there is adequate space under and around the laptop to allow unobstructed airflow into the cooling inlets.

 

It could also be the fan regulator, they can malfunction and cause the laptop to power down. Two of my friends had this problem and it turned out to be the regulator