Access to RDS Server via Remote desktop connection

Need to know more about the config and use.  Are you connecting from the internal network or remotely?  Is there an RDS Gateway? Is there a firewall between the RDS server and you?  How many users and licenses?  What error message do you get when you try to connect?

That said, the first thing to do would be to check the Event Viewer logs on the server for any errors showing up there.

Thanks Hypercat.  

5 user RDS server and can't connect on the internal network or via VPN.  it wants to create the connection and asks for credentials and then the unable to connect to the remote computer error appears.  
It has been working for the last year and a half but stopped when I switched ISP's however I still use the same router and there is no double NAT. 

Are you certain that your ISP's equipment (modem/router, etc.) doesn't have some filtering turned on that would cause this issue?  Since it seems to have started when you switched I would certainly question that if you haven't already.  However, if it's internal as well as external it points to something on the gateway server or between the gateway server and the other servers.  If it asks for credentials, then you're connecting initially to the gateway, so it's behind that.

I assume you've checked all services, etc. to make sure everything is good there.

What is the error that appears?
Do you have another system on that network to which you can connect and from which you can access services, eventlogs , on this system to see what might be going on, possibly triggering a reboot of the RDS system.

There is little information included in your question on which I can go and guestimate what might be going on.

try accessing the /admin
mstsc /admin /v:yourrdsserver
This is an Administrative access and only an administrative account will be allowed to connect.
See if that helps.....
Presumably you are not getting an error related to licensing.
When was the RDS deployed? When was the RDS licenses added?

The questions are a kitchen sink, I am trying with as many as  come to mind that might help guide you to what to look for,

Make sure RDS server has latest Windows updates. Reboot RDS server.

Are the Windows 10 workstations fully patched?

Are the users members of the Remote Desktop Users group (on the RDS server)

Check the Event Log on the RDS server look for errors at the exact time and date stamp that a user tried to connect. More than likely it will tell you why they cannot connect. If the Remote Desktop app prompts the user for the login then that means the RDC connection was initiated. So that event would be logged.

Did you purchase and install RDS CALs on the server? It runs in trial mode when you first set it up and enable it, it will run for 120 days.
To check how many days are left in your trial, open a command prompt as Administrator and run this command (one line)

wmic /namespace:\\root\CIMV2\TerminalServices PATH Win32_TerminalServiceSetting WHERE (__CLASS !="") CALL GetGracePeriodDays

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