The answer is:
However – you can’t because your admin it totally not working..
So the other answer is to go to the core_config_data table and set the path dev/js/merge_files to 0 (zero)
Sometime, that row was not even in the core_config_data table.
The final solution was to add a new row, setting the path to dev/js/merge_files and the value to 0.
Finally clear the cache and reload.
You are done.DOWNLOAD SOLUTION HERE