On phone with HTC support, performed these steps:
Removed battery from phone.
Kept out for about a minute.
Put battery back in.
When boot finishes, touch App button (bottom left of HTC Inspire screen)
Then Settings.
Applications.
Manage Applications.
All.
Maps
Clear data
Return to normal use.
Voila , my navigation kicked right back in.
Hope this helps someone else.
Removed battery from phone.
Kept out for about a minute.
Put battery back in.
When boot finishes, touch App button (bottom left of HTC Inspire screen)
Then Settings.
Applications.
Manage Applications.
All.
Maps
Clear data
Return to normal use.
Voila , my navigation kicked right back in.
Hope this helps someone else.