thank you for offering support, but I just let it ran, and had dinner :-)
After dinner I found out it had finished (nearly after 2 hours). All works well. This was in DW 2014.1
This morning I installed the extensions for dreamweaver 2015. After starting DW again the 1-2-3 popup became visible, but this time the downloading and installing of files went quick and easy. After restart DW all was well!
Not sure what caused the problems yesterday (because then I also tried installing in DW 2015 with no succes).
Anyway, I can go back to work now and be happy.