ok try using an ethernet cable to connect the PC's to the ports at the back of the router. Then disable the wifi part of the router & PC's but then you wont be wireless. This should test to see if you have something wrong with your wireless settings

Do you have them all on the same SSID?
Whats the connection signal like on the wifi?

Ok since you have SP2 running turn that off becasuse it will block programs and apps trying to connect or send. Other wise go to the device connection and then go to its firewall settings and enable all services on that firewall. (Sorry im having to do this from memory as my 3 month old 420W PSU bewup lastnight, so you may have to look round for what im discribing)

Ok for the protocols and services you should be running on your computer are. (off the top of my head)
-TCP/IP
-IPv6
-Microsoft file & print sharing
-Network monitor

There should be about 4 items in the list. Make shure you have them enabled for that device, not any ethernet connetion on your machine if you have multipule connections.

Why do you start your IP allocation so high in the list.
I havent delt with the setting called AP isolation so you will have to try it.

When i get my computer up and running again i will try to recreate your problem and do a walk through for the solution if i can.

search for the computers on the network. Type * in the search field for computers and uses on the network.

hope this helps....