PC restarts unexpected

[ElDude]

I am running a:

cpu: i5 4670

mobo: Gigabyte GA-H97-Gaming 

ram: 1 x hyperx fury 8gb ddr3-1600

gpu: GTX 750ti

ssd: Kingston a400 240 gb

psu: EVGA supernova 650w 80+ gold

 

My computer restarts unexpectedly, sometimes right after it POSTS, when Windows is loading, sometimes when I am using it. I already tried resetting the CMOS, and I don't think it is a HW problem because it never restarts will I am in the BIOS, only while using Windows. I also tried installing Windows again from different USBs and the same problem appears. My BIOS version is F7 which is the latest for this mobo.

 

[NoMansLand]

Does it just shut down or turns off and on automatically?

 

If it's Restarting when it POSTS this could be a Hardware Fault, CPU / RAM / PSU - Begin with the PSU.
 

[ElDude]

13 hours ago, NoMansLand said:

Does it just shut down or turns off and on automatically?

 

It turns completely off and the turns on automatically. It is definitely after it POSTS because the speaker only sounds one short beep which according to gigabyte it is OK, and it only restarts when it starts to load windows or when I am already running windows.

 

I already ran memtest and it had no problem. 

 

How should I test my psu and cpu?