The new Service Release one KB3081424 just destroyed my Insider Preview system. After it installed and rebooted, Windows 10 would not start with an error about inaccessible Boot Device. Several attempts at Automatic Repair have failed. Reset failed part way through and undid what it was trying to do. Attempt at System Restore from Advanced Troubleshooting Options reported the Restore Failed with error 0x8000ffff, but upon restart it allowed me to log in and System Restore reported successful completion. I switched to Slow Ring for updates and am shutting that PC off until MSFT puts out a fix. Also, can I reinstall my Insider version from the ISO made by Create Media? Can I delay updates on this Insider version of Windows 10 Pro? Thanks for any help
Try booting into a windows 10 iso and doing shift-f10 to bring up cmd prompt. Then run: bcdboot c:\windows or bcdboot d:\windows It depends which letter it's using for the system drive. could be e: as well.. Make sure to boot uefi if you're on a uefi system and have lang match as well. If those don't work you can try: bcdboot c:\windows /s c:\ /f ALL /l en-us where c: is letter of system drive and en-us is replaced by whatever lang-code is appropriate for your system.
Thanks for the reply. For now I got it running with Advanced Troubleshooting > System Restore, which reported it failed but it actually did restore to 7/27. For now, I will wait a couple of days before starting the PC and retrying SR 1, and if it does the same failure again, I will try your recommendations.