Hi,
-What is the exact/complete error message?
I would suggest trying this; you won't lose any of your data:
a) Plug the Surface in to the power supply. Turn off the device by holding power button down for 6-10 seconds
b) Tap the power button to turn it back on.
c) Once the surface logo appears, wait for circling dots to appear and then hold power button down for 6-10 seconds to turn device off again.
d) Repeat steps 2 & 3 until the surface logo appears with words underneath saying “Preparing Automatic Repair”
e) Recovery mode will start.
f) At the Bitlocker screen, tap “skip this drive”
g) Tap advanced options
h) Tap Troubleshoot
i) Tap Refresh
Refresh will take 10 to 25 minutes (if it takes longer, even much longer let it finish); when it's done the Surface should go to the login screen. I hope it resolves the login issue, please let us know.
Note: The apps that came with your PC or you installed from Windows Store will be reinstalled, but any apps you installed from other websites and DVDs will be removed. Windows puts a list of the removed apps on your desktop after refreshing your PC.
Let us know the status of the issue. If you need further assistance, please post back. We will be glad to help you.