Hello, welcome to Wiichat. The easiest thing for you to do would be to call Nintendo, they can probably fix your problem within minutes.
Some suggestions though: erase any connection settings you have on your Wii and start a new one; make sure you do a wireless connection and do automatic settings. Before doing this, it would be a good idea to turn off your router and unplug it for a bit, wipe all the settings off of it and start clean.
Make sure your security code on the router, if it is enabled, is allowing the Wii to access.
Try channel 1 or 11 on the router (I think these are the channels Nintendo suggests, but could be wrong).
Again though, calling Nintendo is the easiest way to get things up and running...they hear things like this every day and this is why they have customer service operators. Anyway, hope you get things working.