Go to Game Settings and make sure your sound is completely disabled, IF YOU ARE ON A PC WITH NO SPEAKERS CONNECTED.
If you are on a laptop, try playing some music, or a youtube video or something. If audio works, don't mess with the Game Settings for Audio.
You might need to install the "DirectX End-User Runtime Web Installer" from Microsoft, if you are using Windows XP or higher.
You also might need to install some of the Microsoft Visual C++ Redistributable packages, if using Windows XP or higher.
I have the ones from 2008, 2010, 2012, 2013, and 2015 installed (both the x86 and x64 versions of each).
I forget which one(s) RebirthRO needs.
You can google search for them.
You can also try rebooting your Modem, Router, and Switches.
If all else fails, you might have to wait for up to a week before you are no longer being Rejected from Server.
Same thing happens to me, but it is super rare. Usually only lasts a day or two.