Phil, does the same thing happen if you (temporarily) turn off responsive?

(if this works you could complete your task, save your work, then turn on responsive)

Are you saving before attempting to preview? Are you editing the template structure? Headers and Footers? Page?

Esahc,

Thank you for you quick response-nice that it came from a fellow Aussie. I am on the resolutions and response design page. I have the save button options unchecked. Button needs to be set to resposive to enable edit button to be oprable. I am able to edit and press Ok Button in the dialogue square. If I then click on either the save button or the Ok button at the top of the page the computer hangs, so I have use off button on computer. and have to start again If I change back to the desktop button then I can proceed BUT when I come back to this page I find the values have reveted to the original value. I hope you can help further.     

Phil

If you start a new project you will easily be able to change the desktop resolution, so it sounds like the complexity of your site. I'd reckon something in your imported site is causing the issue. Large images? Blank cells on pages?

I cannot recreate your problem, but you might like to try changing your project to desktop only, modify the width and then save it.  If that works, turn on responsive and modify the lesser resolutions.

Esahc

I have tried the switch to desktop only but this does not change the hanging problem. To do a delete each file and test would be too lenghty an excersise , so I wiil create a new website and link the existing one as an archive.

Thank you for your help