[globaleric]

Quite likely the iPad doesn‘t „see“ the PC anymore because of one of the mentioned changes. Either the provider change involved getting a new router which is currently preventing that network connection for some (security?) reason, or the Windows reinstall involved a fresh PC Firewall setup currently blocking any incoming connections from the home LAN.
Or the iPad got a new IP address because of the router swap, which is now blocked by the Windows Firewall.

You could install the free „Net Analyzer“ utility on the iPad and then (while the PC is on) run a Scan on the LAN. The network connection between iPad and PC would only be ok if the PC appears in that result list.