Of course you first need to check there is nothing wrong with the server. If you can’t find an issue there, what else can you do to regain access?
De you have Avast?
Avast has a nasty habit of blocking my server when things update. Head across to Avast Firewall is Blocking Network Share. Windows Report explains very clearly how to resolve this issue.
Sorry there is no picture for this. I don’t know what I’m allowed to screenshot for copyright, so you get a blank screen for this one.