MSTSC - mouse input works, but somehow keybord input is locked. How to unlock?
Please go to:
Control Panel\All Control Panel Items\Ease of Access Center\Make the keyboard easier to use
Turn off Filter keys and check.
Firstly, I assume your keyboard is working fine for a non-RDP window.
While the RDP window is active, tap each of the left and right Ctrl, Shift and Alt keys. Also tap the Windows key, the Menu key (the other "new" key added for Windows) and any other modifier keys.
Faced the same issue. I rebooted the remote machine (a poor solution). That worked for me. Did not want to spend a lot of time in the net looking for a solution.