Thank you for your reply ahoeben.
I see what you mean, the top bar is transparent indeed. I never knew it should not look like that. I have not created a theme or anything like that, Cura is purely as it "came out of the box", with only the scaling addon from the Marketplace installed as an extra.
Pressing the Activate button does not make the control buttons for any printer appear.
My suspicion is that my machine does not have enough memory to make Cura work correctly (even though I do have 8GB of RAM in my 64-bit Windows 7 machine). Could a lack of available memory lead to symptoms like we see here?
Best regards,
Evelien