BitLocker

[Mike Lynch 0]

I have a MS windows Surface Pro tablet. This morning on shutting down it asked me (as is often and normal) to update windows and I clicked update and shutdown. This evening I switched on and the blue screen came up BitLocker - enter the recovery key etc., and it listed a 30 alpha / numeric recovery code starting with A- - -- tapping on the line to enter that code brought up just a numeric keyboard i.e. no letters and I can't see any way of getting up an alpha numeric keyboard. I plugged a keyboard into the USB port and it lit up and i can use that to type in numbers but no letters appear. The blue screen does offer other options e.g re install windows NONE of which work.
Anyone got any ideas on how I solve this ?