Here is my code, somebody please take a look at this, I really don't get it. It's so simple... yet..

Try to run it on your N900 and then select Menu->Location->GPS
It does not work..
If you comment out this line:
MainWindow::showFullScreen();
The GPS button will work.

Also try this:
If you uncomment this line in the constructor:
//startGPS();
the locationing works right away, no problems.
(you can see this if you go the the desktop and look at the statusbar or wait for a fix and the menu will change to coordinates)