Computer shuts off on its own

I decided to post this to save you all some time and money if you ever are faced with the situation I was in last week.

If your computer is shutting itself off, rebooting on its own, or turning off unexpectedly after being on for only a couple hours or less you may have a dead or dying power supply.

My specifics:
After having the machine on for around 48hrs straight I powered it on last week Tuesday morning to get some work done. The machine rebooted itself after 2 hours of continuous use. I thought nothing of it and continued to work. 2 hours after the reboot the computer shut itself off. I left the machine alone for about 5 hours. That evening I turned it back on and got 90 minutes of use out of it before it turned off on its own. After that I'd be lucky to get 30 minutes of work. There was no pattern to what the machine was doing when these shut down episodes would occur. The machine could be working a bit, a lot or idle, clue #1

After one of these episodes I would have to turn the power switch in back on and off and try the power button the front multiple times before I could get the machine back on. clue #2

I decided to search google to find a fix to my problem. Most of the answers I found pointed to an overheating processor. I installed speedfan to check my core temps, on that front things seemed fine, maybe a couple degrees centigrade high but nothing that would cause an emergency shut down, clue #3.

I also read while doing my misguided research that you should be able to see scorch marks on the processor if you’re having overheating issues. So I removed the heat sink and took a look no scorch marks clue #4. After reinstalling the heat sink with some new thermal liquid speedfan showed the temperature to be a bit lower than before.

I also read that its possible for the video processor to perform auto shut downs if its overheating so I checked that processor, applied new thermal liquid and then replaced the card with an older one I had laying around. The problem persisted, clue #5.

After 5 clues that this was a power issue I should have taken the hint but instead I replaced my motherboard and processor at this point. The problem persisted, clue #6.

It is at this point that I got a new case and power supply and now all is well again. Personally, I hope that you all, my dear readers will try this much much less expensive fix around clue #3. Learn from my mistakes!