Admin and Register site issues

Hello everybody,

I have a small problem with the admin site. 
Every time I try to go to the [MY SITE URL]/admin site I get an error message.
Error message: “Whoops, looks like something went wrong.”
The same message I get even if one is registered on the system.

I hope you can help me, since I can not use the old system any more.

Regards,
Kasternikus

Did you delete the user set up by the installer? What do the logs say?