In case this helps anyone:

""New pc with a fresh install of AC. Game installs without issue and you are able to authenticate, able to select a character but opens a blank window with only the pack displayed. Did you remember to reset the modem/router?""

The new pc has a new computer name but the modem/router most likely has the old computer name in the settings. If you like I use port forwarding, the modem is trying to send packets to a machine that may no longer exist. Compare the computer name usually found in the router under "my network" with the computer name found in Windows "control panel>
system>computer name".

If different names, reset the modem to factory default, reboot router and pc, log on to router, re-enter the port forwarding for Asherons Call, log on and play.