Help with DS wireless stuff?

Now, me and my friend just have a simple DS, it's not a lite or anything. Before we were connecting and were able to do all kinds of stuff with the DS, but now we can't even get a signal. We've tried multiple times, and it used to work before, but we can't even get a signal to connect our DS's. They aren't lites or anything, but it used to work and we used to have a signal before, but all of the sudden we don't anymore. Any help on this would be great Thanks!