I tried this to solve my problem with the "re-indexing the internal search"
1.Delete all the files included in the App_Data\Search\folder
2.Go to Admin->Search Admin and click on the Re-Index Content Button
3.Go to Hosto->Host Settings->Other Settings-> Search Settings and click on the Re-Index Content Button
3.Go to Host-> Schedule , open the Search Site Crawler and run the scheduling action by clicking the "Run Now" button
4.Restart your IIS
After I tried all this I still get no search result.
I have to reset it, cause I need the most of the search results.
Thanks a lot for your help!