Though the downloader may show 100%, please allow some time for it to fully complete.
You may be able to fix this by running the downloader and pointing it to the same saved location so that it may scan and download any missing files. We became aware of an issue affecting the previously available German and EU English versions of the digital install downloader for Diablo III, which would not download all the necessary files.
Whether you repair your previous install or download the entire game again, it's necessary to use this new downloader to install and play the game when it launches.
If you try running the Diablo III file and nothing appears to be happening, check to see if the Windows Service for Secondary Logon is enabled. This service being disabled may also cause the system to appear to hang during the "Updating Setup Files" portion when run.
In almost all cases it has to do with an overlay that the 3rd party programs use that causes the crash.