Thanks for the responses. I understand now that it was not the new router's firewall but something about the new network's settings on the computers. The computers were on when the new router was installed, and they could still access the database on the main machine until they were restarted and the new network dialog came up. I did make sure that they were work networks and the advanced sharing was set up properly. After that, the clients could then access the main computer and its files, but AC kept giving them the "cannot locate SQL database" message. Navigating to the main computer's .xml file just kept returning the same error message.
When I bridged the modem and put in an older router, the clients could again access the SQL database. I'd like to try again to get the system to work with the new router/modem.
All computers including the main computer are set to obtain IP address and DNS servers automatically. What network error could allow the computers to see and access the main computer on the network, including changing files, but not connect to its SQL database? If IP adresses or subnet masks are wrong in ipconfig--how do I fix them?
Do I need to give the main computer a static IP? I haven't done that before. How should I do it? Can I just make it's current IP address fixed in its TCP settings?
