On one of the wired PC's visit
http://192.168.1.1 default user/pass when asked is admin/admin (unless you changed it yourself)
Then proceed along to the "Wireless" tab heading near the top, then under "Basic Wireless Settings" you can change the channel. Try channel 1, see if that works, try channel 6, and finally channel 11. (then anything in between if they don't work) the channels i said are widely used, and don't cross over in terms of frequency, which makes them alot more stable.
It may look something like the attached picture.