Keyboard and mouse wont work

Hi,

My pc powers on and the monitor displays fine, but the mouse and keyboard aren't powering on. I tried a different keyboard with the same results. The pc stops at the press enter to boot screen but I can't press enter. I installed a new hdd this morning and it started fine afterwards. Its only after a few hours that the pc crashed and the problems started. I used my cellphone and usb charging cable in every usb port and there is power. Any help would be appreciated. Thank you