Airport Extreme connection timeout issues

Help! I am getting a "connection timeout" on laptops trying to connect to my new Airport Extreme wireless router. I also am unable to connect, or get the same message, when trying to connect my Wii for streaming Netflix and the PS3 for online gaming (my son is really upset about this).

All worked fine for the first few weeks after buying the "square" Airport Extreme; the "connection timeout" messages just started appearing about three weeks ago.

Apple is no help; there also doesn't seem to be clear answer to this problem on various discussion threads. Somebody must know how to deal with this!!!

Also: I have never been able to get my base station to recognize an Airport Express.