Built two new PCs for work and they won't connect to the 2830n - either via WiFi or Ethernet.

The 2830n has latest firmware.

The PCs connect to the 2830n V2 in our other office. the 2830n V2 at my house and they connect to my phone as a hotspot.

My phone will connect to the 2830n and an old laptop we have will also connect to the 2830n both WiFi and ethernet.

Any ideas? I've lost days to this issue.

Check that the IP addresses they're using aren't already assigned to another device / MAC address in the [LAN] > [Bind IP to MAC] list?

Beyond that, try a basic network switch in between the Vigor 2830 and the computer, though that's less likely to help if wireless also doesn't work.