Usb ports and monitor display don't work

hi all, newcomer here, been playing around with pc's for about 5 years now but stumped by a problem with my wifes pc. she bought a new desk last night and unplugged the pc to swap it to the new one, i set it back up for her and it started fine with no problems, 10 minutes later she complained the cursor wouldn't move, i checked the batteries in the wireless mouse and they were fine and then found the keyboard wouldn't do anything either even though all the lights were fine on the remote. we switched the pc off and sent it into rundown and tried rebooting a few minutes later but the monitor claimed it had no input and the lights weren't showing on the keyboard/mouse remote, i switched the usb leads and checkes all the connections but nothing changed. could this point to a motherboard error? as there's definitley power to the units so the psu is fine. any help would be appreciated. dan.

Hey ,welcome join in ,but your pc problem is just beyond me .