Connect to another PC in my house

I have a wireless router at my PC. I have a wireless adapter connected to the PC with my backup drives. I normally Map the backup drive and then use FreeFileSync to mirror my drives to the drives in the backup PC. Nothing has changed at the "backup" end. At the main PC end I upgraded to 64-bit, so need to setup again. Using the default IPs allocated by the router. I can ping the backup PC. I...