HELP! I am a newbie to all of this

Our phones don’t work. I am the closest thing to an IT guy we have here. Our current IT guy disappeared. We’re trying to get our phones working.
We have the following:
Teliax
Asterisk
Trixbox
FreePBX

Polycom phones.

Callers calling in get the initial greeting, but when they push the button for an extension, the extension doesn’t ring. And after about a minute of silence, it goes to that extension’s voicemail.

And when we call out, call cut off after 15 minutes (almost exactly 15 minutes).

I don’t even know much about Linux, so I really could use some help.

THANKS IN ADVANCE!!!

I don’t know what registering means. The boot up and show the name, extension number, etc. I can call phone to phone. We can call out to “land lines,” but the phones drop out after exactly 15 minutes.

Thanks for your help.

Are your phones registering? Can you call from phone to phone?

People love to help other people who like asterisk and freepbx but generally they don’t completely offer to setup your system unless there is some kind of compensation. I know freepbx offers paid support and there seem to be thousands of voip services online.