Computer unexpectedly restarts with shorter frequency each time

[monumental]

I've got a computer that randomly restarts even with no peripherals attached, even from within the BIOS. After swapping out the RAM, hard drive, and video card I RMA'd the mobo and it's still occurring with the new mobo. I've used a multimeter to test all of the pins on the PSU and everything is within tolerances. Within the BIOS I've watched the voltages, CPU, and system temps and don't see any spikes before it restarts.

Definitely hardware related because I've wiped two different hard drives (one HDD and one SSD) and reinstalled the OS with the same results. I've ran chkdsk on the drives with no errors found.

Here's what happened most recently after installing the new mobo. I reinstalled the OS on a different drive and the install went fine. Computer was up and running and I downloaded avast and malwarebytes and ran scans with no issues found. I then began downloading updates for the OS and in the middle of a download it rebooted with no warning. After that it becomes increasingly unstable and Windows startup becomes corrupted to where it can't be repaired. It's gotten to the point where the computer will restart, POST and then immediately restart again.

The only thing I haven't swapped out is the PSU and the CPU, but like I said I've tested the PSU with a multimeter. A couple weeks ago I took the whole thing in to Best Buy because I'd just given up and hoped the Geek Squad could do something. They hooked a PSU tester on it and said it was good so that it was probably a bad mobo.

The CPU is an i7-920. Not overclocked now though I did some in the past though nothing crazy. It's got a Zalman CPU fan on it. The temp as reported in the BIOS and mobo LED is around 32.

Anyone have an idea on what's going on or how to further test?

 

[brispuss]

Seems it may be either the CPU or the PSU that is faulty.

First make sure DIMM's and video card are seated properly!

Similarly make sure all cables are connected properly (power, data, monitor, CPU auxiliary, video card auxiliary) and in the correct slots.

Remove CPU and check it and the socket for damaged or missing pins/pads. Re-seat CPU and its cooler carefully and evenly. Don't over tighten cooler mounting screws.

If there are continuing issues, then try another known working PSU (borrow from friend, neighbor etc if necessary), and/or try the PSU in another computer.