Recently my rather old desktop stopped booting. The LED in the power switch would come on and the little green light on the mobo would light up. The case fan and cpu fan would start to spin for about a second (if that) and then stop spinning.
I pulled the PSU and tested each pin and they all appear good. I then started by plugging stuff back in one at a time and found that when the hard drive is plugged in (ATA HDD) is what appears to stop the system from coming on. With the HDD not powered (I left the ribbon cable attached) the system POSTs just fine until it comes time to read the boot media.
Is this a PSU issue or a failed hard drive? How can I further troubleshoot to narrow it down?