Some games work and some dont

hi

my sons Xbox is very strange is he 10 so has a child’s account so unsure if this is the reason. he always used to play COD and GTA and all them adult games. but for some reason they are not working now on his Xbox? we put in Disney Rush and that’s fine. he cant even play Fifa and i’m sure that doesn’t have an age limit? please help, we are so confused. i’m not sure if its the actual drive and if so how do we fix this? or is it a case of it now being dead? ive done some googling and have checked he has blu-ray installed and he has. please any advise would be amazing. kind regards, a very confused mummy lol