Backend/dashboard not visible after admin login

I have logged into the backend of my site at www.example.com/wp-admin, but after logging in, i don’t see the regular menus on the left side any more.

What happens is that my site loads (frontend) with my, the admin logged in, but I don’t see the menus on the left any more.

Does anyone know what the problem is?

Thanks for any help in advance.

Cheers!