Update 3 :Update 2 :
Unfortunately same problems again. It is completely random, but i noticed a couple of patterns. 1st When i press stop to a movie and get a black screen, i can see the gui by pressing back button and then the left arrow (no alt+tab or alt+enter are working). 2nd Sometimes when i press stop, movie stops for a while and then i am getting no video but audio is continuing. At that point the only think that is working for me is put pc to sleep and resume. (stop, buckbutton, arrow keys, ctrl+alt+del, alt+enter, alt+tab are not working)
by playing around with madVR settings, i changed display mode to switch to matching display mode when media player goes fullscreen and restore original display mode when media player leaves fullscreen. Also I completed the display mode textbox with all compatible display modes that my tv supports. From then i started playing and stopping, about 30 movies and all working ok (lets see if it lasts).
BTW. I found a very comprehensive set up guide for madVR with great explanation for all settings (Although its in kodi's forum
HOW TO - Set up madVR for Kodi DSPlayer & External Players
Greece