A few common problems..
1. You misstyped the SSID
2. If using WEP or WPA you mistyped the Password. (try reconfiguring the router (temporarily) without WEP or WPA
3. Your wireless router is using MAC filtering and the new 600's MAC address is not in the table.
4. Your Router (or whatever it is that is providing your IP address) is out of leases.
5. If using WEP you selected the wrong index.

LT

I had the same problem. Two existing laptops connecting, but the new 710m won't.

This is what worked for me. Try changing channels, I finally connected all three on the default Channel 6, running 64 bit WEP.

Try it and post your results.

sorry, I just got back to this. I'm using a mac airport. Could that be the problem? if so is there a correction?

oh, and to clarify it was working fine--although didn't get great reception--and suddenly stopped