2012 Mac Mini upgraded from Mav to El Cap is now invisible

[Howlinmoon]

We have two iMacs running el Capitan and a 2012 Mac Mini running Mavericks.
All three machines saw each other fine (the other two always showed up in each machine's finder side bar)

I upgraded the Mac Mini (AFTER making a CC clone of it) and when it came back - it was no longer accessible from the two iMacs.

I have tried connecting directly via it's IP (via finder - connect to server ) and it always just times out.

The Mac Mini can see the other two machines just fine - but they can not see it.
(The two iMacs appear in the Mac Mini's finder side bar - but it does not appear in theirs)
(and yes - I can access the iMacs fine from the Mac Mini...)

Before biting the bullet and reverting back to Mavericks (and hoping that fixes things) does anyone have any other suggestions?

We use the Mac Mini as our media server - and previously would just use screen sharing to add files to it etc.

 

[nightcap965]

Have you checked your Sharing and Security settings on the Mac mini?

 

[Howlinmoon]

Have you checked your Sharing and Security settings on the Mac mini?

gah!

I feel like an idiot.

I *assumed* settings such as those would have been carried over - and never even bothered to check.

*sigh*

They were defaulted...