using Macmini server, loose connection, repeatedly

I have been using a mac min server latest model as my server to place all digital music, and running Logitech media server on it.

I also use an ipeng to access and control the digital files. I have three squeeze box units that are in my house. all linked thru cat 6 cables thru a home network.

I repeatedly lose connection soon after i start any music, it looks the computer goes to sleep and the units can no longer access the logictech media library.

Currently the energy settings are put computer to sleep after 15 mins of disuse. But the computer should not sleep if the logitech media server is being accessed and is running.

Any one has the same issue, any recommendations.

thanks. navid