While playing a multi player game the Wii llost connection to the handhelds and they are no longer able to connect on reboot etc..
I've tried a different disc drive and my handheld controllers are fine.
Try re-syncing the controllers.
You do this by opening the slot on the front of the wii under the reset button and opening the battery slot on the wiimote.
Now press the red sync button on the Wii and then on the remote in order to do the re-sync.