In many cases all you need to do is remove the batteries and re-install them. Be sure your batteries have life and are usable.
In some cases a firmware update is required. If the battery reset above doesn't do the trick, follow out firmware link here for updates http://www.vervecycling.com/firmware-updates/
If you've successfully installed the latest firmware and are still encountering problems. Email email@example.com for Recovery Mode update instructions. They're a bit more complex.