Question PC Problems: BSOD, random Reboots and No Video Signal

[john-9023]

Build:
i7-4790
MSI z97m
2x 8GB ddr3 1600MHz Corsair Vengeance
Nvidia gtx970
Corsair cs650m

For some time the PC had freezes with buzzing sound ending in BSOD. It was necessary to reboot (via the button on the case), in some cases even twice because after the first one there was no video signal.
Then one day after turning on the PC, it restarts two or three times by itself and when it manages to "stabilize" and turn on there is no video signal.
I tried to restart both with the button on the case and directly with the button on the motherboard but it does not restart and on the debug display of the motherboard the series of codes always ended with b2 which, for the little I could understand by looking at the manual, corresponds to "late south bridge initialization".
Then I tried to do Clear CMOS via the button on the back of the motherboard and connected the cable to another display port of the GPU.
After that, I tried to turn on the PC and after a message on the screen that said to press F2 to continue it started normally.

What could be the problem?

Thanks

 

[Paperdoc]

My speculation only - NOT a "for sure"! I suspect the PSU is weak or failing. I note that your PSU's power rating should be enough for that system.

 

[john-9023]

Now every time it is turned on there's no video signal and the reset buttons (both on the case and on the motherboard) don't work so it must be turned off using the start button on the case.
Then it needs one or two Clear CMOS via the button on the back of the motherboard before being able to start normally.

I don't know what to do...

 

[Misgar]

I don't know what to do...

If the buzzing sound came from the PSU, change the PSU. The noise might be from a failing fan, or some other PSU component (inductor, transformer) on its way out.

 

[john-9023]

If the buzzing sound came from the PSU, change the PSU. The noise might be from a failing fan, or some other PSU component (inductor, transformer) on its way out.

For buzzing sound I meant the audio of the system that start making this noise after everything freeze.

 

[Misgar]

It's hardly surprising the audio fails when the system crashes.

Check the CR2032 battery with a multimeter and replace if below 3.00V. It's probably something else though.

 

[lava2]

RAM, HDD, SSD, motherboard, processor, or PSU can all be responsible for the blue screen crashes. your computer display the BSOD if it's overheating due to dust, defective fans.

 

[john-9023]

The BSODs are continuing, sometimes even when I have not opened any heavy software or I am not stressing the hardware in any way. It happened a few times that BSODs occurred even just because I moved the case a little by tripping on it slightly or for connecting the USB cable of an external HDD behind the motherboard.

Then after the BSOD I restart the PC using the button on the case and when it restarts sometimes it doesn't give video signal and if I try to restart it again with the case button (or directly with the button on the motherboard), the PC doesn't restart.
In this case the only solution I have is to turn it off by holding the power button on the case, then turn off the PSU, wait a bit, turn the PSU back on and press the button behind the mobo to clean cmos. At this point I try to turn the PC on with the normal button on the case and hope it posts. Often it doesn't and I have to repeat the procedure doing a couple of clean cmos until, once turned back on, it finally posts and starts normally.

I tried to test some of the hardware to exclude them from the cause of the problem.
I ran memtest86 with 4 passes and didn't find any errors.
Checked SSD and HDD with CrystalDiskInfo and they're all good.
About CPU and GPU, they are often under load for some 3D or video rendering and encoding with Handbrake and crashes and BSODs happen randomly, even when they're completely in idle so I think they aren't causing the problems either.

Someone said me that probably the capacitors of the motherboard are dead and this could be the cause.
What do you think?