One thing I could only tell you, Microsoft added since Vista a lot more security features, but with Windows 7, I don't know if it was there with the 7000 build, the certificate features, Windows maybe tries now to do a connection with certificate with a computer that don't even know the existance of a such feature, I know you probably look at it already, but make sure all security measures are gone, close Windows Firewall/Windows Defender, Right-click on Computer, Remote Control, if you got a router, try to do a DMZ with your Computer, did you try to connect to another computer inside your LAN, what about VPN (if you are using it) make sure everything are set with the right protocol, if you are using VPN, if you map a network drive to your computer and then you do a file transfere, is it slower than normal? If yes, the problem is maybe the VPN, otherwise, you must find something about the RDP, I didn't look at it, but maybe Windows changed the port number for it, maybe it's still using 3389 port, but as a secondary one while the primary one is blocked.
You can try to change your listening port, follow these instructions :
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Good Luck