Some observations:
I usually have XP running
not in XP-stil but in classic style.
Today, after booting the machine and starting Pelles C, I have the triangle toolbar and the new-project-dialog shows all the individual icons. I could close the ide and restart it, all remains ok.
So I decided to test if an reboot has any effect.
After the the reboot I got suddenly XP-style on my desktop automatically!
I don't understand this at all.
I started Pelles C: all ok.
I closed the IDE and changed to classic style: all wrong.
I changed to XP-style and started the IDE: all ok.
I changed to classic style (without closing the IDE): all ok.