What could cause intermittent connection between computers connected to a router?

I have 3 computers running windows 7 connected to a wireless router and each computers are assigned with dynamic ip in the range 192.168.0.30 - 192.168.0.253, subnet mask 255.255.255.0, gateway (router) 192.168.1.254.

I have problem connecting from one pc to another, ie. when I try to ping the other computer, I sometimes get reply, and sometimes i get 'destination host unreachable". I have tued off windows firewall.

What could be the cause and how do I troubleshoot to find the problem?

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