Sorry, I don't speak German, but here are some diagnostics in English:
First of all, you should know you are using an OLD version Imagevue X2. We launched new
Imagevue X3 1-2 years ago, which uses HTML5 and does not depend on the outdated SWF plugin:
https://forum.photo.gallery/viewtopic.php?t=8618
Your X2 website loaded fine here:
If it doesn't load for you, are you sure you have the SWF plugin installed in browser?
Other than that, your server is perhaps a bit slow. From here, it took almost 1 minute to load your background image before X2 could display:
Your background image is 1.6 MB:
http://www.canactivity.de/iv-config/the ... 024neu.jpg
So apart from the slow load, as long as you have the SWF plugin installed, your website does eventually load.
There is one more issue. It seems your start page is not configured properly, so it doesn't load any images on the start page.