If I remember correctly, when this happened to me I called Microsoft (o the joy of talking to people across the world from you

) because I thought it was my xbox, because nothing else was being affected. In the end he said he would conact my ISP(I have no idea of proof he really did), but after about a week it stopped and I haven't had problems since.
Another tip, on your Wii, try totally re-setting it up with your network. As in, scan for new networks, choose yours, enter the WPA, ect.
Hope that helps, Basically from the first paragraph, if re-setting up the network doesn't work, call your ISP.
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