Hi Chris,
It looks like the microSD card has become corrupted and needs to be re-flashed. If you have a PC or Mac to hand, you can download the 'balenaEtcher' app and the BB1 image file from the Brennan website.
If you repost this request on the new Brennan Forum we can offer further advice from there. This website is no longer in use for day to day problems.
Peter.