Hi Alexa,
Unfortunately the original screens aren't repairable in a way that they last. The connections on the screens are also very brittle and can easily break preventing the screen from working at all, which is most likely what has happened to yours and why it is no longer working.
I used to own MG Rover Custom Car Parts and used to do repairs on these. Working with a automotive LCD specialist manufacturer I had new screens developed and made with a improved design to solve the issue with lines appearing on the display and fitted 400+ of them worldwide.
I sold the business on but the new owners do still offer this service. They can supply the screen to you and also can install it for you. I would recommend getting it professionally installed as fitting the screen requires soldering the 44 tiny micro contacts which are the ones that can break if you're not careful.
They can be contacted here:
https://www.facebook.com/MGRoverCustomCarParts
Thanks
Rick