SPTH:

Depending on the program, keybd_event won't work in all cases.

It is common for game programs to use functions like GetAsyncKeyState and GetKeyboardState. These two functions completely bypass anything you might try to do with SendMessage and keybd_event.

Also you are calling keybd_event without properly setting all the parameters. Set the scan code to the correct value and follow it up with another call to send the release key.