OK, where to start....

For reasons I wont go into,I want to attach 2 external hard drives to my old desktop PC running win 7 ultimate and still get access to them from my macbook air over the network. The PC is connected wirelessly to the netgear router using a dongle. I have a Macbook Air which is connected to the netgear router via a wired connection. Both work fine in connecting to the internet (PC has full signal).
Both have sharing on for files and printers, but they cant see each other ???

Is it something to do with me already having a `homegroup` set up on the PC ?

I have googled the issue, and all i seem to find are how to change the settings ....which are already correct...