PC in boot up loop, wont start

[SimonH1971]

I bought a "Infin8 Vesuvius" Intel Core i7 4790K @ 4.6GHz Quad GPU Extreme Gaming PC back in 2015.

About six months ago my pc started to take three attempts to boot before completing the boot sequence and going to the windows desktop, so no problem.

About three months ago the PC started to randomly shut down while I was using it.

Now when I try to start the PC it just keeps on restarting. Every third restart I get the bios window come up, but pressing F12, F9, End and Delete does nothing, the screen goes blank, I see my mouse pointer momentarily and I can move it around for a few seconds and then it restarts.

I have read the forums for similar issues, but cant find anything definitive. Any help would be gratefully received.

Is it worth returning it to OC to get fixed? Or better to use a local repair shop?

The PC cost me 3,300 so its not something I can laugh off or start willy nilly component replacing I think.

Things I have tried so far:
Cleaned the cooling units and fans and check they run correctly
Checked the PSU powers up properly
Removed 1 memory stick and then the other, and tried both in different slots.

 

[SimonH1971]

Well, I just got my new power supply and fitted it and its still doing exactly the same.
While its booting up I am looking at the digital display fitted to the motherboard.
On first boot it says 8 and doesnt budge from that number - all I get is a black screen and then restart
On the second boot it says 8 and doesnt budge - all I get is a black screen and then restart.
On the third boot it goes through a series of letters and numbers : A8, A6, 96, 77 etc... the motherboard start up window comes up but pressing F12, F9, End and Delete does nothing. It restarts and goes back to the first boot up.
If I left it it would continue this loop rebooting all day long.

Other things I have tried: removing the GPU and tried booting it up with the onboard graphics. Does the same
Tried switching the memory sticks over and trying every combination, single and double
Tried booting from one hard drive then the other, with a boot up cd - but it did the same.

I am open to suggestions please. Whats the next unit I need to try replacing? OR do I need to admit defeat and send it to a repair shop?