dvr recording some shows and not others but showing they are recorded

A few days ago our DVR started having issues.  We go to watch a show that is recorded and it either turns the screen black and is not playing (even though shows the full hour recorded) or it plays the first minute and then freezes and will not play anymore of the show.  Then it will record the next show on the same channel with no problem.  There are no weather issues or anything else going on to disturb the program, in fact a few of the times this has happened we have been watching something else and seen the show recording and on with no issues but then when we go back to watch it, it will not play.