So many things going wrong, at a loss. (Help appreciated)

[ShintaroK]

Okay, so where do I begin? I suppose I'll list my system specs
Motherboard: Asus Sabertooth z77
CPU: i5 3570k (OC'd to 4.3GHz)
Cooler: Corsair H100i GTX
GPU: Gigabyte GTX 980 G1 Gaming
PSU: EVGA 600W Bronze
RAM: 2x4GB(8GB) Corsair Vengeance Pro DDR3 1866Mhz
Storage: 1TB Seagate Barracuda, 1TB Western Digital Blue
Case: Corsair Air 540
OS: Windows 10 Home

So basically, my old motherboard failed on me, and i purchased this motherboard secondhand from someone on craigslist. I also replaced the RAM, and RMAd the psu. So basically those 3 things are the newest parts in my system.
When I first installed the motherboard, for a few weeks, it would give me tons of blue screens. (Even without the overclock applied) Mainly on startup. So I read that with new motherboards you are supposed to do a reinstall of windows, so I sort of did that, I did it through the "settings" in windows 10, i dont think it was a fresh install, because i do not know how to perform one.
but i did have to re enter my windows key, which was given to me by microsoft.
The blue screens pretty much stopped and I didn't notice anything for awhile.
Until I turned on my PC, and mid-boot, it shut itself off. It has done this a total of 3 times since that has happened.
And furthermore, my PC is very, very slow to boot. usually after the windows logo it will go to a black screen without a mouse cursor, but today it went to that black screen after the windows logo, and stayed there. And I waited for several minutes and it just would not go past the black screen. So i turned off "fast boot" in BIOS and it finally went past that screen.
I am sorry for the long post but I am at a TOTAL loss here guys.
Could it be the PSU? The motherboard?
I should have a bit of spare money in July, although that is a month away..
Thank you very much in advance for any help.

 

[Gamesmasher]

Well, though I'm not a complete expert on this myself, I recently had to get a new motherboard and CPU to fix my computer and you usually can't get a new motherboard without re-installing windows. In my case I got the same motherboard as the one I broke but it didn't work(either because the CPU was DOA or the motherboard had a different BIOS version and didn't want to run), so I got annoyed and said F*** it and got a new hard drive and OS copy of windows 10 (where I literally just got done installing everything before getting on here to ask a question) and a better mother board and CPU. So far it works perfect so you could try that, it's a little bit more expensive and too me a month of work (part-time) to get the money to fix it but I think it's the easiest way. You might be able to get away with just getting the OS though as I saw there were options that MIGHT help in this situation.