It sounds like your network name is different on the 3 computers versus the one. Make sure they all have the same network name or group name. If they are different, technically they would be on different networks and wouldn't be able to talk to each other.
Hope this helps. Good luck
I'm new to this - I just had a wireless network installed - we have a total of 5 computers, but Roadrunner claims they can only connect 4 - but that's later.
Right now my issue is this - my computer (the one that has the printer connected) is directly connected to the router - the other 3 are wireless. Those 3 are networked together but my computer does not show up - it seems to have a network of its very own. I've run the set up several times - same results. How do I "merge" the wired and wireless network? The provider is of no help - that's home networks is not what they support.

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