My sister gave me her Konka 188UI DVD player. It had a relatively new DVD in it (a sesame street one) that played perfectly. My problem is that any DVD I rent when I press play, the screen states 'invalid operation' and won't play it. I tried the code selection process already posted (i.e. door open, 6, 6, 6, 6, etc.) but the DVD player doesn't respond when I press the numbers. I am pretty sure that altho the remote control is a konka, it isn't the original remote. I know nothing about DVD players, does anyone have any suggestions as to what I am doing wrong?