I have an Orange Mobile broadband dongle. It haseen working quite happily for mionths but suddenly I get Internet explorer cannot displat the page and the diagnostcs tell me that the DNS is wrong ior doesn't exist. Any ideas.

DNS is not part of Windows 7 nor is it a Windows 7 function. DNS is short for Domain Name Service and is usually provided by your ISP. So, you need to contact your ISP to ensure you have all the correct settings for your internet access.Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.

It gives you a DNS errors, it means that either the DNS server is down and it is not getting response from that or it is not able to connect to the DNS. As rightly said this is a DNS issue not a Win7 issue