PC shuts off after a few minutes
So the background is i'm building a new PC, and in preparation i took all my current parts and put them in an old case. When i powered it on it shut down when windows was loading. Then i tried again and it started up fine but shut down after 10 minutes or so. I tried just reinstalling windows on it and it shut down midway through. Tried taking out RAM sticks, sound card, seems to always power down after around 10-15 minutes. I currently have it powered on in the BIOS in the PC Health status menu to monitor the CPU temp and it's sitting around 36C and hasn't shut down going on an hour now. Any ideas what the issue could be?
Intel Core 2 duo e8400