PC won't turn on, peripheral lights flashing intermittently

[eternalsnafu]

My PC was disconnected from the outlet for a few days and now it will no longer turn on. I used the paper clip method to check the PSU and the fan worked fine.

The weird thing is, the peripherals (mouse and external HD) connected to the back panel and flashing on and off but it seems like they cannot sustain the power. I suspect that is the same reason the PC won't turn on.

The PSU is Corsair GS500 and the motherboard is ASRock Z87.

Any advice?

 

[hiyabusared]

Try a different PSU and then see if it boots

 

[eternalsnafu]

Tried a different PSU but the issue still persists.

I guess it's the motherboard then?

 

[CompGee]

Unplug all peripherals and retry.