Ubuntu server stops working after a while

[Vendetta Hasard]

 After around 4-5 hours, my ubuntu server running plex media server stops responding. Here's all the server does when crashed:

 

-the server screen stays black with no command line interface displaying.

-keyboard is not responding/seems completely cut from power

-cannot access server via ssh

-plex server doesn't work anymore like all other services

-Computer still runs but can only be fixed by holding the power button pushed to force shutdown the computer and then reboot.