Sorry, I didn't see this till now.
Quote from: frankmehlhop at Apr 17, 2013, 04:07 AMHi frogabog,
Quote from: frogabog at Apr 11, 2013, 10:10 AMTry clearing the cache manually by deleting all the files in the core/cache folder.
You mean at the server? Please have a look at the attached screen shot (cache.png). This folders look important to me. You mean to erase theme?
YES. You'll want to do this first when you run into issues so get used to it. These files/folders will be reloaded as soon as you visit the site again. In fact, you could even delete the core/cache folder itself and it will regenerate (although I never do, I delete just the files). Be aware of which folder you're deleting though and make sure it's deleting core/cache/fileORfoldername and not core/fileORFoldername (I did that once... not good. MODX can't function without it's core)
I have a feeling this might be your solution, so I'd like to find out if it works before pursuing any other suggestions at this time.
If it doesn't work, please check the error log (manager menu -> reports -> error log and tell us what you see.
I even re-instalated the hole modx again and installated the package for TinyMCE and again the TinyMCE is not showen. 
Something else to try is to install CKEditor from package management and set the RTE to that editor instead of tinyMCE. Do you see RTE in resources then?