Playback error-can't get arround it

Server Version#:
Player Version#:

I have the latest server and client, I believe. My media is on a 3TB external drive. I have the server on a Dell laptop, running Win 10 (i just replaced the HDD with an SDD, 1 TB). Everything else seems to work OK, but not Plex. The client displays the many icons for the movies I have, but when I click on one of them, the screen shows Playback Error. This occurs on all four of my libraries. How can I fix this?

Hm how long has this been happening because I have been using Plex for years now and yet a few days ago this started happening and now, today, no matter which file I select, and no matter if I try to play it on the browser interface or through my Samsung Smart TV, which is how we usually watch stuff from Plex, it will not play. I just get the flashing icon on the top left of the TV as if Plex is waiting to load the description info of the file, the meta data I mean…but it never magaes to and eventually it says Error. In the browser I get a similar thing. It spins and spins and seems to be trying to load the mopvie or tv show and then eventually it says
" Playback Error

Content is unavailable""

I am stumped. And gutted that now I have to use thatr slow piece of erm, excrement, windows network to stream some media to the TV…if it works!!!