Do you have a link to your site and maybe additionally a screenshot of how the navigation should look? Would be easier to help troubleshoot the issue with a link. Thanks.
Dear Will many thanks for your message. You have helped me to solve the problem without realising it – I hid the sidebar and increased the window to full screen to take a screen shot for you and… hey presto!! it returned to the previous format. Then I reduced the window size more on Chrome and the same happened. If you check out http://www.vinergia.com/wordpress you can see what I am doing. Thanks for your help!
Cheers,
Robert