Dell monitor has an on-screen shadow

Earlier I was trying to install the software for a USB-Parallel printer cable and I've noticed my monitor has just developed a "shadow" behind all text and pictures. It's a light grey colour double shadow appearing behind all text.

As if all the text is out of contrast/focus.

Any ideas what might be causing this?

Thanks!

I've just tried the monitor with another PC and the monitor still has the same problem.

So I think there must be something affecting the actual monitor rather than any PC resolution problem. I think...

Is it still out of focus if you use any of the on screen control menus (for setting horizontal, vertical alignment etc.)? Is there a degauss option (button or on screen menu option)? If so try that and see if it helps. What model of Dell monitor is it?

I've reset the various screen adjustments such as brightness/contrast colour/display settings back to factory settings as it hasn't helped.

I also used the vertical/horizontal buttons which didn't affect the blurriness.

I don't see any specific degauss button.

It's a Dell 2407WFP-HC such as the one here;

http://www.pcpro.co.uk/reviews/128864/dell-ultrasharp-2407wfphc.html

The monitor was perfect previously, so I'm guessing there must be some software/adjustment problem rather than there being an actual problem with the physical monitor.

Just in case anyone here develops the same problem, I've just discovered what was causing the shadows!

The cable which connects the monitor to the PC had become slightly detached at the back of the monitor.

Once this was pushed in fully it stopped the shadows.

The connector should have small thumbscrews which should be tightened to ensure that this does not happen again.