No BSOD, just full reboot cycle whenever trying to access files or scan hdd

[TC1019]

Hey guys, I REALLY need help.

My pc boots to desktop fine, but it will suddenly restart when:
- accessing my Downloads folder (I moved all the contents of that folder in Safe Mode [where it was fine] to a different folder and the problem followed it)
- sometimes accessing other folders (but not nearly as much as the Downloads one)
- connecting to the internet for more than 3 or 4 minutes
- trying to update my BIOS drivers
- and trying to scan with Malwarebytes (in both normal AND Safe Mode!)

When it reboots, it just turns right off. I've disabled Automatic Restart. No BSOD, just a full reboot. With no BSOD, no error codes, right?

I've tried pretty much everything. I've unplugged all peripherals and my second hard drive. I've reseated everything. Tried with just 1 stick of RAM (using both of them). I put in another known working power supply. I even Refreshed my Windows. The problem remains.

I've tried scanning and fixing hdd with chkdsk...ugh I'm just so frustrated.

specs:
Window 8.1 Pro
I7 4790 cpu
MSI H81M-E33 mobo (everything default apart from the network driver)
Onboard VGA
Seagate Constellation 2tb hdd
16 gig DDR3 ram (2x8)
And I've tried it with both 600 and 480w psu's.

Please help!

 

[axe0]

Hi TC1019,

Does it also turn off when you have the very minimum connected (a good PSU, 1 stick of RAM, the CPU, nothing more)? This will normally display a message that no operating system is installed, but you won't see it and that's fine. We only want to have just enough connected for the pc to start and see what happens, nothing more. You'll want to do this with the case open to see what happens with anything that gives light and/or moves.

Have you resetted the BIOS and checked the power voltages in the BIOS related to the PSU, CPU and RAM?