Windows cant talk to each other!!!!!!!!

I have about 20 stores w/ 2 windows XP workstations in each for POS, the software i use is called retail pro, the program is installed on wks1 and wks2 needs to connect to wks1 to run the program.

i got a call today, one of my stores cant get thier systems to talk to each other, i checked every thing i could think of, Firewall, etc etc…