A question: You say your modem is brand new. How about your router? is that new or are you using a combo modem/router?
First thing I would do is turn off your cell phone, the turn off your modem, then turn off your router (if not a combo) wait about a minute the turn the devices up in this order: Your modem, your router, and make sure each device cycles up fully before turning the next device on. By cycling your devices until they are stable with lights solid etc. (some modems have a connection light that flashes which is fine) then turn on your cell. The phone will find your network ssid and you then click on the network name on your phone and connect. Make sure the password for your network is entered exactly (upper and lower case and numbers etc) if the modem and router have cycled ok you should get a stable connection.
Please note any devices at your home that were connected via wep or wpa security should re-find your network and connect without you having to set the up again.
I would also have removed the network name connection for your network from the Pantech so it can find the wireless network fresh.