I can't see other computers on the network

I have a MAC Pro Tower connected directly to my D-Link DIR-655 wireless Router. There are 4 PC's on the wireless network, and my MAC is the only one that is not a PC. The PC's can see each other, and they can all see my MAC. I cannot see any of the PC's. Any suggestions would be greatly appreciated as I would like to be able to transfer photographic files, and word files from the PC's to the MAC.
Any suggestions and/or direction is really appreciated.
Thank you.