Question Unsure if issue with CPU or Motherboard

Nov 18, 2020
Hi all,

So I've run into issues recently with the PC and I've narrowed down the cause to either my CPU or Motherboard but can't tell what is causing the issue.

So the issue is when the PC turns on, it'll keep going for ~7 minutes and then shut down and immediately boot once again. The majority of the time after this boots once again, I'll have no display. After this happens, I'm not sure if it POSTS as I don't have a MB speaker (one o the way). If I shut down and boot once more, the same issue happens where I'll have no display. This can only be resolved for shutting down for a decent period of time, usually about an hour where the same will happen once more when the system is turned on once more.

What I've tried:
-Removed the GFX card, using onboard
-Removed 1 and both sticks of RAM
-Since this began, I've replaced the power supply with a new supply as I had originally taught this was the issue due to some other indicators pointing to a failing supply
-Disconnected any peripherals and HDD (SSD still connected)
-Replaced the CMOS battery with a new battery
-Used different displays with board GFX and onboard
-Checked if the issues occurs while on the BIOS screen, ruling out OS issues
-Taken apart the system completely, fully cleaned and everything reconnected/re-seated
-Checked temps, these are well within parameters before the system crashes

The above comes with the same results everytime,

What I can't do:
-I don't have another system available to check components
-I don't have any spare components I can use to swap parts
-I can't check MB beeps until the motherboard speaker arrives (unsure even if I'll get beeps)

MSI H81-P33
Intel i5 4460
8GB (4x2) Ballistix DDR3 1600 CL9
MSI Radeon RX570 8GB
Corsair ATX 550w
Samsung 750 EVO 250GB SSD
Seagate Barracuda 7200 1000GB SATA

She's an older system so I don't wanna be paying a couple of hundred on a new CPU, with a 1150 socket none the less but would be willing to pick up a new Motherboard. While any help to resolve is appreciated, I've accepted that parts are needed so primarily I'm looking to see if anyone has any advice on how I can narrow this down further.

Thanks in advance!