HP 8300 SFF Randomely Shutting Down

[Asama]

I haven't had this PC longer than a year, first and foremost. I haven't done too much on this PC, I primarily use it for gaming (League of Legends). It was fine at first, but after a while it began to shut down randomely, and without warning. No "Shutting Down...", just power off. I kinda think it might be a power supply issue, but I don't see why or how it could possibly be. After it shut down the first time, it began happening more frequently. I gave my computer a long while to rest, (a few weeks) because I didn't have time to look into the problem. I've moved into a new place now, and I started using the PC again, and it was good at first, but the problem arose again in the next few days. I've tried a multitude of things, software-wise. For about 40 minutes after startup, Task Manager will show 100% disk usage, and it may even extend passed that. 

[Asama · Accepted solution]

Turns out, I solved this issue, if anyone cares.

After a long witchhunt, I ended up around the CPU GPU area. Now I understand that checking CPU and GPU usage under BIOS isn't really accurate to the CPU/GPU usage when your computer is actually operating and completing tasks.

I resulted to attempting to underclock my CPU to see if that would work. I attempted to benchmark, but while executing the benchmark, my computer shutdown AGAIN. Then, I knew the CPU was the problem. Whilst trying to underclock with the Intel XTU application, I noticed something with the name of Intel Turbo Boost.

As it turns out, Intel was automatically overclocking my CPU the whole time. I became interested in disabling it, but the option wasn't made available from the app. So I went to Google for answers. The Googl-ing was successful, and I ended my hunt here https://www.tautvidas.com/blog/2011/04/disabling-intel-turbo-boost/. This fixed all my problems. 

TL:DR; https://www.tautvidas.com/blog/2011/04/disabling-intel-turbo-boost/ fixed my problems.