If the server accessible with RPC (basically, if you can access a shared folder on it), you could free some memory and thus let the RDP service work properly. The following windows native commands can be used:
To get the list of memory consuming tasks:
tasklist /S <remote_server> /V /FI "MEMUSAGE gt 10000"
To kill a task by its name:
taskkill /S <remote_server> /IM <process_image_name> /F
To show the list of desktop sessions:
qwinsta.exe /SERVER:<remote_server>
To close an old abandoned desktop session:
logoff <session_id> /SERVER:<remote_server>
After some memory is freed, the RDP should start working.