PLEX Media Server

I am running Zorin 15 and have PLEX installed as my media server on a Dell laptop. I can't figure out how to keep the computer to stop going to sleep. It can sit idle for hours but when I start streaming a movie it stops every 30 minutes or so, seems to be a random thing as some shows I can get through the whole thing and others I have to wake it up or sign back in more than once. I have tried to extend the sleep interval in the Power Mngt page but nothing changes.
I stream the content ROKU on my TV if that matters.

TIA