Unidentified network - no valid IP config after new modem installation

[Seven7seven]

Hi guys,
Backstory: I had an issue with my wireless connection at home so asked AT&T to fix it, the technician came, installed a new modem, set up a new network on my main computer, everything was working and he left.
Problem: I have a second computer that is connected to the network via belkin av500 network adapters and half an hour after the guy had left that computer realized that something in the setup had changed and is now refusing to connect the the network. "Unidentified network" is the official message it gives me... and something about not having a valid IP configuration. The powerline units seem to work fine, humming along with green lights. Any ideas as to where the problem might be and how to fix it?

 

[T_T]

Just a thought...When the tech set up the new modem, he may not have set it up using the same IP address as the one before.

Is the computer in question able to see the new modem/router's SSID?

If not, try disabling the third party wireless software, and then re-enable Windows Wireless Zero. See if it detects the SSID of your AT&T router.

If that doesn't help, login to the router and disable your security, temporarily, of course. Now see if you can connect.

If the computer in question can see the SSID, it may be just a matter of reauthenticating.