I know that the admin panel pulls it's css from the Simplicity theme, so make sure it is installed. It could be a corrupted install, or something related to server requirements. One big one is, if you are running php version 7, you will need to drop back to 5.6, or 5.5.

You can check the right side of this page to make sure the server requirements are met. I'm not good with server side issues. I rely on my host to help with that.

https://developers.oxwall.com/hosting