Hi Krys,
Based on the troubleshooting you've already completed, including verifying the BitLocker key, attempting Startup Repair, checking System Restore, and running a reset that keeps your files, it appears the device may be stuck in a restricted sign-in state rather than experiencing a simple PIN or password issue.
At this point, a practical next step would be to perform a clean Windows installation using Surface Recovery Media from another working PC:
Please ensure that you backup any important data, including Documents, Pictures, Videos, and more.
- Create a Surface Recovery USB using Microsoft's Surface Recovery tools.
- Boot the Surface from the USB drive.
- Reinstall Windows from the recovery image.
- Sign in with the same Microsoft account after setup completes.
If your personal files are still important and accessible, consider backing them up from the recovery environment before proceeding with a full reinstall.
I hope this helps get the device usable again. Please let us know how the Surface Recovery process goes, and the community will be glad to assist further.
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