Double clicking doesn"t behave in 2007

Hi, I just upgraded to 2007.
It is quite a change in interface,
but, on one of my computers double-clicking a table or a form or any other
object in the navigationwindow doesn't open them.
Right-clicking, I get the little menu and there I can open it.
What on earth can cause such behaviour?

please enlighten
tia

michiel rapati