Guys... Enderal is installed within your skyrim directory and it uses the data of Skyrim and an own modified .esm (It's not Skyrim anymore... ).
Of course you can't launch Skyrim as long as Enderal is installed. That's why the Enderal Launcher creates a backup of your previous Skyrim installation.
The Launcher has a button to simply change between Skyrim and Enderal (change installation).
Just watch this video.
What you have to do now (Read everything before doing anything):
Run the Enderal Launcher. Click "Change installation" and delete Enderal completely (do not archive it!).
Skyrim will be automatically reinstalled. Go to your Steam library, rightclick on Skyrim, select "properties". Go to "local data" and click on "Verify Integrity of game cache". Steam canns your Skyrim and installs missing files.
If that's done copy the Enderal Launcher into your Skyrim folder and run it. Install Enderal again from the installation package.
If it's installed again you can use the "change installation" button to switch between Enderal and Skyrim. It's also explained in the video which I linked above.
You could also setup a dual installation of Skyrim and Enderal.
Watch this video.