Motherboard sometimes cuts power and reboots on startup

[freemini]

The title doesn't make that much sense but neither does my problem. Sometimes, though at least once per day, when I want to start my pc it starts normally (all fans, hard drives and so on start) but the monitor does not detect any signal and then after 3-5 seconds it shuts down, with the sudden-lost-of-power sound. It then stays off for another few seconds and starts normally. I think it might be because it is OC'd but it is stable so I don't see why that would be an issue.

i7 2600k@4.5GHz

Asus P8P67 Deluxe (B2 stepping)

GTX 580 stock

Windows 8 x64

Bonus question, my old PC doesn't shut down at all (it just starts back up right after I shut it down, even with the power button). The only way to make it stay off is to turn off the PSU and turn it back on. Any idea what the cause might be? My idea was the power button but that looks fine, so I have no idea about that ether. Let me know if you need extra info.

[sze_nian]

I'm not good in these but i would try to help.

Whats your power supply?

[EightyFourPercent]

I had a similar issue with several Asus motherboards. 
 

Is the TPU switch on? 

What about the EPU setting in bios?

Have you tried clearing the CMOS? 

I have heard about the marvell SATA might also cause this issue so try disabling that if its not in use?

 

Let me know if any of that helps.

[Taipeek]

Looks like MOBO problem rather than PSU since MOBO is controlling PSU when to go on and off.

The first probem looks like your MOBO is configure something or do some test like when you change your CPU it does something similar or when you do automatic OC - the mobo is testing some configurations of clocks and restart even more than once like this.

The second is really weird to me. Is this happening the whole time you have the PC or it suddenly started to do so?

[freemini]

I'm not good in these but i would try to help.

Whats your power supply?

Corsair HX850W

I had a similar issue with several Asus motherboards.

Is the TPU switch on?

What about the EPU setting in bios?

Have you tried clearing the CMOS?

I have heard about the marvell SATA might also cause this issue so try disabling that if its not in use?

Let me know if any of that helps.

TPU is switched down, I have no idea which way is on or off, it doesn't seem to indicate on the board.

EPU settings to disabled.

No, didn't clear it.

Marvell controller is off, I don't use it.

Looks like MOBO problem rather than PSU since MOBO is controlling PSU when to go on and off.

The first probem looks like your MOBO is configure something or do some test like when you change your CPU it does something similar or when you do automatic OC - the mobo is testing some configurations of clocks and restart even more than once like this.

The second is really weird to me. Is this happening the whole time you have the PC or it suddenly started to do so?

It isn't automatic OC, I manually set the multiplier at 45, voltage is 1.325.

[colonel_mortis]

Just try turning the OC down a bit and see what happens.

[EightyFourPercent]

TPU is switched down, I have no idea which way is on or off, it doesn't seem to indicate on the board.

EPU settings to disabled.

No, didn't clear it.

Marvell controller is off, I don't use it.

Try changing the TPU switch, it should be off by default but you never know.

Save your OC settings and try clearing the CMOS it might help.