Wanderer

My apologises it is an Alien Megahero DVR circa 2017/2018

I am having a problem with the playback, namely i can only see on playback one camera out of 4 at a time. I have real time from all 4 cameras, but when trying to see more than one camera on playback i get one camera with 3 black areas corresponding to the other cameras. If i click on any of the black areas then that displays the corresponding camera, but again only one camera is displayed/showing. This happened a month ago, so i rebooted thinking it would solve it but after a week the same occured. Is this a software/programme problem. I am not connected to the internet. Thanks for any advice.