Hi there, have you tried a different player like MX player or vlc? If you don't have them installed, you can download them from the play store. If your files don't play on any other player then the problem is with your downloaded files. If they work on one of the other players then the problem is with your android player. May need to be updated or it may not support the file type of your downloaded files. MX and vlc support pretty much every file type, so if your files don't work on them, then they didn't download properly or are corrupt. Hope this helps.