True I Agree,
there are multiple reasons why you can not join a server or the server do not start up even if done everything alright.
it can be a bad installation, or the update made wrong. 1 small file can make the server share the process of fully running well. It could be a patching not done right. Anything.
Please provide Logs or Output (Both client and Server) so we can see and find out the exact problem.