Since the release of the latest Surface revs, problems are continuing to be reported where the Surface will boot into a screen that requests the BitLocker Recovery Key before it can continue. This issue was also reported with the first revision of Surface devices, however, it was not as widely reported as it is now.
This result can be caused by a wide range of things such as corrupted drivers or Windows Updates not able to install successfully. Whatever the reason, you'd like to be able to get past the BitLocker Recovery Key request screen, but have no idea how to locate this extremely long number.
Luckily, Microsoft stores this number for you in the Cloud. Using a working computer connected to the Internet, just jump out to the following link and ensure you are logged in with your Microsoft account.
When you access this link, you'll something similar to below, except yours will contain the actual Key ID and abnormally long Recovery Key number.
The BitLocker Recovery Key is intended to add an additional level of security, ensuring that only the authorized owner of the Surface can unlock the device and restore access. Unfortunately, if you can't find your key, or your key does not display on the Microsoft account page, you'll need to restore the Surface to factory default settings, i.e., start over.