Windows reboot at startup even after fresh install

A month ago, my Win8 PC got stuck while working, so I had to reboot. After I turn it on, Windows couldnt get started, even after it tried to repair itself, It said that it couldnt fix it. I waited a few hours, and It finally got past the Windows loading screen. It worked fine till a week ago, when it did the same thing and I had to reboot, but this time it didnt worked after many tries, so I decided to format the drive, and reinstall good ol Windows 7, but after a successfull installation, it crashed at the first start in the Windows 7 logo, going on a loop.

I bought a new hard drive thinking that mine might have died, and after another installation process, I could get through the first start. But it was working sooo slow, it took like 10 minutes to get to the desktop, and 10 more just to open the start menu. After I restart, the crash at startup returned.

I dont know what it can be, maybe the mobo died? I tried clearing the CMOS, updated the BIOS, replaced the CMOS battery, checked the RAM sticks, replaced the SATA cables, tried the HDD in the other SATA slots, tested the DIMM slots. Im running out of options here.

I think its hardware related, cause even after a fresh Windows install Im getting stuck at startup

Here's my system:

-Windows 7 and 8
-ECS P67 H2A3
-Intel i5 2300
-Seagate 500gb 7200 HDD
-2x4gb Kingston Hyperx RAM (tried with just one stick)
-AMD HD7870 2gb
-Antec NeoEco 520w

Any help would be much appreciated.

Have you got your RAM voltage set properly in the BIOS? Undervolted RAM can make the system do funny things. Check the voltage for your sticks and set them accordingly if necessary.

I've just checked and they're properly set. I also ran memtest86 on both ram sticks...

What's the specific type of Kingston RAM that you have?

Did you stress the RAM - Test with Memtest86+ for 7 passes or more, or overnight?

Kingston has the best tech support in the industry. Will replace any of its RAM it helps determine needs replacing no matter where you got it.

Did you test the HD with the maker's HD Diagnostic extended CD scan?

Work through the other Troubleshooting Steps for Windows 7 which will almost always reveal the problem.

Before you get a new mobo, try relaxing the timings on your RAM a little. They're specced at 9-9-9-27, try setting them a little looser, like 10-10-10-30 and see what happens. I have a similar issue with my RAM and have to set the timings more loosely to run at 1600. Your mobo might be reading the SPD defaults and setting the RAM accordingly. Also, to run at those timings, your RAM voltage must be at 1.65V.

Hmmm... Maybe your mobo is failing. Did the problems start to happen after the BIOS update? Or before?