Computer needs a usb plugged in to start

[Blitzcrieg]

Computer is about a year old and now has a random issue that the computer will not turn on with the power button. 

 

However when checking everything on the IO i found that if i unplug then plug a USB into the computer it starts up, everything else bar this is working fine with the computer.

[Jasun]

Open up the computer and make sure that all the cables are connected to the motherboard.

[Sauron]

Check inside if the power switch connector is properly inserted on the pins, it may have fallen off if it was mounted loosely. If it's connected correctly, try disconnecting it and shorting the two pins with a paper clip or something similar - if the computer turns on the button on the case is probably broken.

 

The usb thing is probably due to a bios feature, it's probably set to be able to turn on via usb.

[Blitzcrieg]

The power switch was connected, i tried to shorting it with no luck so looks like it the motherboard, but interestingly i can use the power button to turn the computer off, so it must be restringing something from those pins.