whys my ds keep freezing

so today i've been trying to play nintendogs: labrador and friends on my black ds, and as seen its just frozen on the voice input bit over and over again. its really annoying cus the one day i want to play my ds it breaks >:(

my copy of nintendogs and my ds are most certainly not fakes because i got them from cex, however they may be damaged as theyre second hand. also i accidentally froze my ds on bootup a little bit ago because i didnt know that taking out cartridges can freeze the bootup and i was switching the cartridge from harry potter and the order of the phoenix to nintendogs