PC won't power on after I turned off power in sleep mode

So my systems sometimes been acting strangely when I put it in sleep mode, it will sometimes power itself back up after I send it to sleep, and when it does this it's non responsive so I just have to turn off the power at the plug.

This usually results in the PC not powering on in the morning for some reason and after opening up the case and checking for loose cables, it somehow usually powers on again when I press the power button.

That didn't happen this morning. The green LED on the motherboard is on, but no fans spin or anything when I press power on.

Tried: -testing for bad power switch by connecting power pins with screwdriver - unsuccessful -used different power cables, unsuccessful.

Am I going to have to either buy a multimeter (to test psu) or a new PSU?

Mobo: ASUS P5KC PSU: Hiper Power 550W