So sdcard formatting was a long process. I was to impatient, after a long time, the message came back that everything is OK with formatting now.
I have material for a second LPC17 core module at home so I will build it now to countercheck the issues I have.
Thanks a lot for the quick answers!
Could please somebody reply on my question about the backlight of my display. I only have to know if the backlight should be on after startup. If yes I have to search at my hardware, if not I have to search the correct command in the program. I still have to learn a lot, thanks for your patience :-)