The problem is that very ocasionally when PC is powered off and I try to turn it on, it will do nothing. Strangely energy is OK because LEDs inside mobo are ON and also ethernet card. The solution to turn it on was to disconnect PSU from power and then reconnect it again. When I do that PC worked fine except mouse (it was dead). I reconnected it and worked.
More strange is that before this build I had in the same chassis an ASUS M4A79 Deluxe with DDR2 and a Corsair TX750 and it experimented similar issues: randomly PC experienced the same situation with not being powered on even with LED lights inside mobo on. The solution was the same to unplug the PSU and plug it again in the electricity.
With that in mind is not PSU (two quality PSU tested with same issue), mobo neither, nor RAM and I doubt it can be caused by SSD, HDD or GPU.
Can be some type of electric problem with chassis? I'm sure screw and the other things (I don't know the exact word sorry) are placed in the correct holes.
I can try to change the "adapter" that came with my first ASUS to connect different chassis cables (power, reset buttons, etc) to the newer that came with SABERTOOTH. Anyway the adapter look the same.