USB port powers on computer...

[azuzu]

Recently rebuilt my computer; replacing Motherboard, CPU, RAM, and graphics card. This new build has an odd hiccup i cannot work my head around. The power button is only capable of turning the PC off, it will not start the computer as it used to.

When I was plugging in my Keyboard, the PC turned on and booted right up. It doesn't matter which of the 6 USB ports I use.

 

[RememberThe5th]

Have you actually screwed standoffs? Thats an sign of an short somwhere.
Try to breadboard PC.
Put it on desk bare, without case, connect it up and try to see if the issue persists, if it does try by removing component by component, eg. one ram, HDD, trying another PSU (If you have spare).

 

[gabi014]

What motherboard do you have currently?