cannot get live view...

Hi, I've been using my k7 with pentax A 1.7 lens and Vivitar macro focussing tele converter mc 2x. Up until tonight it's worked great but tonight when i set up the camera I can' get the live view to work and am unable to press the shutter. I tried everything with the lens only and it all works fine but as soon as I put the tele converter back on, no liveview, shutter won't work! I'm not the most experienced photographer and am probably doing something wrong, but what? Suggestions much appreciated. Ben.