I just got my D54250WYKH a few days ago and have this problem in random. With the hint from this post, ,I used a small USB extension with the keyboard and mouse receiver to test each USB ports. To my surprise only 1 out of the 4 ports worked, a little led light up indicated power via that port. The led was off for the other 3 ports, indicating no power via those port.
I may conclude this is a problem with the board which doesn't have enough juice to power all 4 ports.