Videos won't play on anything



I'm using an iMac connected via ethernet to my router with a 4TB Lacie HDD for all my content. Whenever I try to play any video on the PLEX server it won't play. No matter the format of file. I've tried on tablets, roku, computer, laptop- nothing works anymore. Everything worked fine and seemingly over night now nothing works. Music files play fine it's just video. I've even tried to set up a second library with my laptop- still doesnt work. Any help would be great. I have mp4, mkv and avi video files. None will play.