Please post below your Operating system and if your are using a 32 or 64 bit machine.
A couple of things to try:-
. Run KnightOnline.exe in compatibility mode and see if that works.
. Open your HShield folder in your client and run HShield.exe in compatibility mode.
. Download Microsoft Visual c++ Redistributable Package - 2005 and above. Download both 32 and 64 bit versions.
. Check for any Windows updates you are missing.