The reason I ask about security is that this should be left turned off until you have a reliable connection.
Okay -- there should be a quick start leaflet which came with your router. Run through that afresh. In particular take a look around the router's user setup screens for a wireless setting with a name like Access List and disable that.
Also look at wireless mode and match that to your computer(s) -- mixed mode may be a safe bet.
You might also look at this setting in Windows:
Check TCP/IP Properties.
Start, Connect To, Connection, Properties, Scroll Down TCP/IP and highlight, click Properties and check that Obtain DNS and IP address automatically are enabled.