System won't boot into W7 partition - BSOD

My system dual-boots to W7 and XPx64 courtesy of EasyBCD, but today when I restarted my PC, which normally boots into Windows 7 Home Premium x64, I got first a screen showing "autochk program not found, skipping AUTOCHECK" and then a BSOD w/STOP error c000021a {FATAL SYSTEM ERROR} The Session Manager Initialization system process terminated unexpectedly with a status of 0x000003a. Tried to boot to Safe Mode instead--same error.

Thankfully I re-booted into this XP x64 partition, and from here I can see the W7 partition from explorer, and googling my errors I found one idea that suggested the autochk failure caused Windows to change the boot info somehow. Thinking that neosmart has experts on the boot process, I hope someone has advice for me:

Should I boot from a W7 Repair disc and have it do the Startup repair? ("Automatically fix problems that are preventing Windows from starting").

Is that a good place to start? Will it break my dual-boot setup that I built w/EasyBCD? I have disk image backups I can revert to, but I'd rather try fixing this first of course. Other ideas? :scared:

EDIT: I've since read-into some troubleshooting info here suggesting if I get to this starting Windows then BSOD that I'm past the boot process and the problem lies elsewhere. Is this correct?


Well my last comment appeared correct i.e. that I was into booting Windows thus EasyBCD was not going to be part of the solution.

The most promising hits I could find on this problem was that it was a Permissions issue. But from the XP x64 boot side the Windows7 partition looked like a RAW filesystem (not NTFS) to Explorer thus I had no access to Permissions.

Then I booted to a Repair disc and got a Command Line and reset permissions on W7's Windows using this command:

iacls C:\Windows\* /T /Q /C /RESET

and although this appeared to function just fine (reset some 89,000 files) it didn't fix the problem.

So I've restored from a few day old image and hope I don't see this one again.
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OK I guess I'd better finish what I started.

After some more noodling today it seems likely this was caused by my fiddling with the MountedDevices registry key in Windows. I have read that you can safely delete that key in its entirety, or delete all the entries to it but the Default entry, and I did the latter except I (probably) deleted also the Default.

Lesson learned: don't muck with the MountedDevices key without a backup at-the-ready. :openmouth:


Mostly Harmless
Staff member
Thanks for sharing the followup with us. Sucks that you had to learn this lesson the hard way!