Resolve File sharing problem

Verify your PCs are on the same network – wireless or wired – and all on the same workgroup (click Start, right-click Computer and select Properties; Is File and Printer Sharing enabled?

Check from the Network and Sharing Center in Vista/Windows 7 – ensure your network is Home or Work. In Windows 7 click Choose homegroup and sharing options > Change advanced sharing settings. 

You can also access it by right clicking the network icon at the bottom right of your computer and select Open network and sharing center. then select Change Advanced sharing settings