PC only goes into POST sometimes and sometimes nothing happens

[Andersxa]

Hello,
My computer has run into a problem lately. When I push the power button on, the computer (mostly fans) turn on but nothing else happens. A red light on the front panel is sometimes constantly lit (hdd light) but my hdd is less than a month old. There's no light in the keyboard, mouse or headset, no monitor is turning on and no lights on the motherboard AFAIK. No beep codes or anything, just the fans and the front panel lights.
Sometimes if I press the reset-button 3-4 seconds after the power button, it actually works and boots just fine into Windows 10. The CPU, GPS and RAM are running no problem, and I don't experience any problems once finally booted. However, it is a hassle even getting it to boot and it is getting more inconsistent every day. Any ideas?

Things I have tried:
- Resetting CMOS
- Reseating RAM and switching SATA-ports
- Booting without any USB devices
- Turning off Fast Startup
- Resetting BIOS to Defaults
- Replace PSU with new one
- Reinstall Windows

Specs:
Intel(R) Core(TM) i5-3450S CPU @ 2.80GHz
RAM 8.0 GB
NVIDIA GeForce GTX 970
Microsoft Windows 10 (build 10586), 64-bit
1 TB HDD WD BLUE
500 MB SSD SAMSUNG EVO 850

Since yesterday, it has stopped as a whole and I have tried stripping it down to basic components. Have tried only CPU, RAM, Motherboard and fan connected to two different PSU's and no PSU starts up. Different RAM sticks in different slots don't work either and the CPU works in an old board. I have even tried another fan, to test if the motherboard can detect it. Also now it won't even boot. It just turns on for 3 sec then off, and then it repeats. Have tried taking it out of the case with paper-clip startup. So to me it seems like the motherboard is faulty, any other ideas?
As I can't boot now I can't check either the hardware monitor or Samsung Magician S.M.A.R.T. or try the SFC. No beep codes by the way.

 

[cin19]

What is your PSU?
Also go into the BIOS hardware monitor section to check the +3.3V, +5V, and +12V. And compared the voltage tolerances from this site to see the PSU is good or not.

Because you said the hdd light was on sometime, may use the samsung Magician to check the SSD and the WD HDD S.M.A.R.T. to see they are fine or not.

And may run the System File Checker (SFC) tool http://answers.microsoft.com/en-us/windows/wiki/windows_10-update/system-file-check-sfc-scan-and-repair-system-files/bc609315-da1f-4775-812c-695b60477a93

 

[Andersxa]

What is your PSU?
Also go into the BIOS hardware monitor section to check the +3.3V, +5V, and +12V. And compared the voltage tolerances from this site to see the PSU is good or not.

Because you said the hdd light was on sometime, may use the samsung Magician to check the SSD and the WD HDD S.M.A.R.T. to see they are fine or not.

And may run the System File Checker (SFC) tool http://answers.microsoft.com/en-us/windows/wiki/windows_10-update/system-file-check-sfc-scan-and-repair-system-files/bc609315-da1f-4775-812c-695b60477a93

Thanks for the answer.
My PSU is the Corsair CX600.
However, since yesterday, it has stopped as a whole and I have tried stripping it down to basic components. Have tried only CPU, RAM, Motherboard and fan connected to two different PSU's and no PSU starts up. Different RAM sticks in different slots don't work either and the CPU works in an old board. I have even tried another fan, to test if the motherboard can detect it. Also now it won't even boot. It just turns on for 3 sec then off, and then it repeats. Have tried taking it out of the case with paper-clip startup. So to me it seems like the motherboard is faulty, any other ideas?
As I can't boot now I can't check either the hardware monitor or Samsung Magician S.M.A.R.T. or try the SFC. No beep codes by the way.

 

[cin19]

The MB has problem, because 1) the cpu worked in other MB, and 2)the PC did not boot with minimum hardware. If you try one more time: only cpu+cooler+onboard iGPU to boot the PC, if the PC will not boot, you know the MB has problem.