[timind]

Last night I turned on the Mac Mini for the first time in a few weeks with the purpose of listening to some music. I had moved my system in to a different room about 3-4 weeks ago and hadn't turned it on since then. So I think everything is connected as before but when I hit play on my iphone remote I hear nothing. After checking connections (look ok), different source (cdp ok), Settings on Mac (seem ok), still no sound. 
Now I'm looking at teh Audio MIDI settings with no problems noted. I go to youtube and pull up a Phish video and the music pours forth. 
Other actions include deleting LogMeIn and XLD from the Mac Mini to see if they are the problem; nope. My daughter suggests I delete and reinstall itunes. The catch to this is I have the music files stored on an external HD and I'm afraid the new itunes won't find them.
Looking for expert advice here. What'cha think my problem might be.
One thing I haven't tried plugging the HD into a different USB port.

[low.pfile]

you didn't mention checking the iTunes Media folder location setting. It may have changed to default local HD instead of your external HD

iTunes > Preferences > Advanced > iTunes Media folder location

if it IS NOT showing your external HD, then just choose it using the CHANGE button

[jarcher]

Is the external hd showing in finder?  If not, unplug and replug until it does (maybe need to wait a bit until it does) then restart iTunes. If hd still won't show in finder, restart computer + try another USB port. If THAT doesn't work the hd may have gone bad. It happens unfortunately - external hds seem to have a few years life these days. Always keep a second copy of your tunes on another secondary hd as well!

[Tyson]

Start Disc Utility and see if the drive shows up there.  If it does, you can open it in Disc Utility.

[timind]

Ok, it was a simple fix, for my grandson. The mini serves music through the computer as well as 2 Apple TVs. There is as setting for "single" or "multiple" users. The setting was on single, with one of the Apple TVs selected.  The button to make this selection is just to the left of the window which displays the song currently playing. It looks like an eject button.
Now I have to reinstall my XLD and figure it out again. Thanks.