You need to enable Debugging.
Settings > Site Administration > Development > Debugging
Set to DEVELOPER Mode and allow error messages to show on the page.
Install the Rocket theme again, and then try Editing. With luck you will get an ERROR that tells you the problem needs to be fixed by a programmer, or just a PHP Warning that something in one of the files is wrong. In which case you will need to make a note of the information where the problem is. The problem will no doubt be associated with the Rocket theme, but the error message should give you some indication of what is wrong.
If you get this far, and you still can't fix it then let me know and I'll try to help.