My controller will not work with my wii anymore

I can think of three things that might be going on:

1. The batteries in the remote have died. Just change them out and you should be good to go.
2. You need to resync your Wii remote. To do this, first make sure your Wii is on. After that, open the slot right under the disc tray of the Wii and remove the battery cover from the controller in question. Press the orangish sync button on the Wii console and then press the sync button on the Wii remote. You may need to do this once or twice for it to work, and make sure you're close to the Wii when you're doing it as its range is limited.
3. Your controller is broken and needs to be replaced. Hopefully this isn't the case.