If it hasn’t been used in a few years, the firmware is very out of date and will not update wirelessly.  First you need to connect the unit via an Ethernet cable to your router and try to add.  If it adds, let it update, then deploy wirelessly.  If that doesn’t work (and there’s a good chance it won’t because of the time offline), you need to contact Sonos support and have them force an update to the unit.