Plex mediaserver doesn't start after installation



Hi, I recently installed the Plex media server on my mac book pro (Late 2009 version 10.11.6) but I can not start it. After finding it in application folder and pressing on it I can see that it opens and appears for a second in a menu bar. Any suggestions how can I solve it?


Here is a short video how I install it:


I have heard of this issue before. Do you have any other software open, check your login items in system preferences. delete them and see if that works. Things like meters, AV, etc


Delete all the login items but it did'nt help. Any other suggestions?