What firewall are you using? The inbuilt MS one, or an alternative?
I've got a reasonably similar set up - the PC is connected by wire to a router, and a Wireless Access point is also connected to the router. My Tablet & Laptop both have wireless cards to connect them to the Wireless point.
I'm using sygate personal firewall (free) on all 3 machines. The only thing that is a bit different is that to get to the PC from one laptop I was able to use Network neighbour hood and just find it.
For the other I had to put \\22.214.171.124 (the IP address of it) into Run, and that opened it up to naviagate. No idea why it wouldn't go in in the first place!
In Sygate you have to set it to allow File Sharing (set the allow on the PC that's the host).
I think that with MS Firewall you can set named IP addressses that can connect, but I'm not 100% sure, as I'm used to Sygate, so have never really bothered with MS.