Thanks for your help everyone I have now got the update sorted.
Firstly, I put in fully charged batteries (just in case).
Secondly, I removed my map card.
Thirdly, I updated in mass storage mode.
Thanks to you all for the help, much appreciated.
Has anyone else had the same problem.
Web updater says version 3.80 is available but when I update it says file corrupt and no update made.
thanks for your help if you can.