Sony :: Vaio Z21 HDMI- 1920x1200

I use a Benq 1920x1200 at work and one at home via HDMI-DVI cable. It worked well until the Benq at home died. I got money back from Benq and bought a Dell U2711 and thought that I could get 2560x1440 resolution on my Sony.

I use Win7. But what really makes me is that the highest resulution on the Dell U2711 I can get is 1600x1200!

I can't choose 1920x1200 from the Screen resolution chooser in Win 7.

I can set 1920x1080 in the the Screen resolution chooser in Win 7, but then I get a dark screen on Dell showing text "unsupported resolution".

Powerstrip monitor info says that 1920x1200x60Hz is supported, but not 1920x1080, so the "unsupported resolution" on Dell monitor is correct.

But how do I make is possible to choose 1920x1200 from Win7?

When I try to use Powerstrip to make resolution 1920x1200 I get the error message: "This parameters you have specified may be beyond the capabilities of your monitor or graphics card. Please recheck the resolution, horizontal and vertical refresh rates, and the pixel clock to ensure they are within spec.". But I can't do anything more...

So how do I at least make it possible to use 1920x1200 on the big 2560x1440 screen?