Thanks for your help every body. I disabled all themes and enables twentyeleven theme instead of twenty twelve. It works fine now. Conclusion... I messed with something I shouldn't have done.
It's probably worth me saying, I wouldn't have messed with the script of a theme unless a plugin had talked me through making changes.
Ralph, thanks for your comment. I think you are offering a solution, but although embarrassing to own up to, the truth is I don't understand what you are suggesting I do. I'd be more than willing to try this - but could you offer me idiot proof instructions?
I'm so fed up and I'm such a novice that i'm going to carry on with twentyelevn and play around with it to make it look how I want it to look.
I must have screwed up the theme or a plug in may have done it. I installed and activated a number of plug ins although I wasn't actually using them.
For your info - if anyone is interested in investigating this further, the plug ins I had activated but wasn't taking advantage of were:
Contact Form 7
Jquery Validation For Contact Form 7
Multisite User Managemen
Bleh. Onwards with the website... after this glass of wine and a few hours sleep me thinks.
Seriously, thanks for your help. I'm learning!