Usually something like this will happen if you've installed some modules that aren't Nameless modules (which has since been improved for the next release).
You should also be able to obtain an error message if you enable debugging in the AdminCP -> Core -> Debugging and Maintenance tab, and then try visiting the AdminCP -> Modules tab.
In that case, if your host provides you with phpMyAdmin to access the database, can you head into the nl2_modules table and delete all modules except forCore and Forum (the first two).
Then, can you delete all folders in the modules folder in your Nameless files except for Core and Forum.
The problem is that you've installed modules into Nameless that aren't Nameless modules, so it's broken the module system.