Cannot RDP to Server 2016 from internal or external

We have a SQL server that the software company RDP's into remotely through our Sonicwall to make changes.  Absolutely nothing has changed configuration wise.  We have always been able to get in remotely from their external IP and from any local machine on the network.

Now all of a sudden none of the internal computers nor the external connection can RDP into the Server 2016 machine.  It errors before it gets to the credentials with "This computer can't connect to the remote computer".  

We can ping it from any machine with no issues using the IP and the server name.  RDP is enabled through the Remote Settings.  It just will not let any machine connect to it and I cannot see any errors in the Event Viewer.

We even rebooted and installed any updates available.  Also temporarily disabled firewall and antivirus and still same issue.  Have no idea how to troubleshoot the connection.
joeshinallAsked:
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joeshinallConnect With a Mentor Author Commented:
Ok, so now it's working after our 7th restart.  Not sure what the issue was but we restarted two more times and it works after each of those.... Case of the Mondays I guess....
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Andy SCommented:
can you telnet on port 3389?
if you can connect that rules out network issues, or the RDP service no running.
If you cant connect, check that there's no blocked ports, that the remote desktop service is running
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joeshinallAuthor Commented:
We have it changed to 3390 but yes we can Telnet to port 3390 on that server with no problem.  RDP service is also running.
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joeshinallAuthor Commented:
After several more reboots it just seemed to have fixed itself.
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