Ok. I am not sure if this will fix it but...
On the windows machine, find the computer name, ip address and name of he printer. Go to the mac and check if all the information is correct. If his does not work, the next thing to check is the actual network. Try restarting your router and modem by unplugging both, plug the modem in, wait 30 seconds and plug the router in. I had a similar problem and that helped. However, try the first thing first, then try the router and modem thing.