My home network is shown in the image below. The problem is that it appears to be two separate networks, so that devices on one side of the wireless router cannot see devices on the other side of the wireless router. My question is: how can I join up the two networks into a single network? I want to do this so that I can transfer files from PC1 to PC3.



Some more detail:
- There are 3 desktop PCs and 1 laptop, all running Windows 7.
- All computers and the TV can connect to the internet.
- All computers can print to the network printer (though PC3 had to be setup manually to connect via the printer's IP address, as it could not find the printer automatically).
- PC1 and PC2 can see each other in the Network and Sharing Centre, but they cannot see PC3.
- PC3 can see nothing beyond the wireless router, which it seems to think connects directly to the internet. eg. attempting to ping PC1 or PC2 IP addresses fails.
- Using the Windows 7 "Home Network" feature, PC1 and PC2 join the same Home Network. PC3 joins a different Home Network all by itself.

Any help would be much appreciated.