dvd+r/dvd-r

Hi again just to clear something up,i have just done a check on my dvd system and have noticed a box unchecked next to dvd+r meaning i cannot play games that are on a dvd-r disc is that correct? i have a box checked next to dvd-r which might explain why i cannot get the game to load that was done on my mums pc and works perfectly.Is there anyway i can check this box i have tried but it wont have it ...help