Switch problems?

I own a small buisness that relies on a server in a back room. I have a wireless router connected to the wall and a switch connected to the routed.

Connected to the switch is several computers and several others are connected via wifi. The problem is that at random times my network will go down. All of the computers can still access the Internet but none of them can connect to eachother or more importantly my server.

Any ideas? Thanks.

If one of the wireless computers can connect to another wireless computer when the network is down. Then the issue is definitely the switch, however if they can't connect to each other its the router.