range rover cruise control
typically there is a SEPARATE button to activate/deactivate the cruise control computer, separate from the buttons that set/accel/coast etc. Sometimes it's on a separate control stalk entirely. If that doesn't work, you're probably looking at a fuse/relay problem or a problem with the cruise control module.
Search Land Rover Range Rover Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Land Rover Range Rover Experts