Have you tried plugging in the front panel wires from your old case back into the your motherboard headers while it's in the new case? they should reach if you put the cases near each other and won't have to take the whole thing apart. If the USB ports work on the old case still, you just got a case with bad wiring. you might be able to find replacement wires somewhere, or if you aren't using the old case at all anymore, just take the wiring out of that and replace the front USB ports.
If your older USB front panel won't work, then it's a problem with your board and you'll have to live without them, or replace the board.