Nothing else connected or plugged in.
Short the power switch pins on the mobo for a second.
If it won't turn on replace the bios battery.
If it won't turn on your down to 3 parts.
So yesterday i was cleaning my computer same as i did before(same steps and same method) and when i tried to power on pc it would start for like 50 miliseconds then turn off and now it wont turn back on. I have tried breadboarding and nothing, ive also tested my power supply on other computer and it worked, but when i connect my microphone to motherboard LED lights on my microphone turn on so that means motherboard is getting power from psu but why it doesnt turn on? Is it maybe cpu?
Hope we will resolve this, oh and those LEDs on microphone would never turn on if the motherboard wasnt connected to psu.