When it falied it must have displayed an error number. It would help if you could say what it was before I can help you.
Normally a number of things can help generaly though such as moving the laptop closer to the wii. Changing the channel the wireless connection is being broadcasted at to 1 or 11. Putting your mac address into mac filtering page on the wireless settings. Though these help for routers though I assume it works in a similar way for the mobile broadband.