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Windows 7: Drive prefixes changed by windows - can't boot

27 Jun 2011   #1

Win 7 Ultimate x64
Drive prefixes changed by windows - can't boot

This is pretty wierd.. Turning on the PC this morning takes me into startup repair, where it can't find any problems.

After a bit of exploration in the command window, it seems my c: drive (40GB SSD) is now called F:, and my data drive (500GB HDD data only) is now called c:
From looking at some of the diagnostic traces, I believe that Windows thinks the system drive is f: (technically correct now), but can't boot from it.

This system has been working fine for several months, and was shut down with no issues last night.

The BIOS can still see both drives, and the boot order is still correct (SSD, HDD).

How do I change the drive letters back to what they were yesterday - without botting into Windows? I've tried the recovery disk, but that couldn't see any problems. Thanks..

My System SpecsSystem Spec
28 Jun 2011   #2

Windows 7 Pro-x64

Could be you lost power overnight and your CMOS battery is dead. How old is the PC? I assume your drives are SATA. Do you have your C drive plugged into SATA port 0? If not and you lost power, the BIOS will assign port 0 as the C drive. Don't know any other way it could happen.

And for sure, I don't know how it booted off your data drive.
My System SpecsSystem Spec
28 Jun 2011   #3

Windows 7 Ultimate SP1 64-Bit

Welcome to Windows Seven Forums.

Have you checked to see which partition is active? Obviously it should be your Windows drive and not your data drive.

You can change it with this free software.

Also, are you able to change the drive letters in Disk Management?
My System SpecsSystem Spec

28 Jun 2011   #4

Win 7 Ultimate x64

Thanks, guys,

carwiz: I built the machine about 8 months ago. I'll try and check the CMOS battery.
Yes, drives are all SATA. I originally had the SSD (C: in some random port (5, i think), but it is now in port 1( ports are numbered from 1 to 6, rather than 0 - 5). I reordered the boot order in BIOS because of the new port scheme, but the same issue happens.
Interestingly, after pulling out the DVD (also SATA), and having nothing else on SATA bus, the SSD (original boot drive) has been assigned D:, from f: before. I can't see why it wouldn't be c:/.
Agree with how it could boot at all without realising it was the wrong drive..

seavixen32: I can't boot into windows to run anything. I get through the boot process until mountmgr.sys, then I get kicked into the repair installation mode.
My System SpecsSystem Spec
28 Jun 2011   #5

Win 7 Ultimate x64

More info:

When I go into System Recovery Options and choose command prompt and do some exploring, I find:

Any ideas?
My System SpecsSystem Spec
28 Jun 2011   #6

Win 7 Ultimate x64

Hi AceInfinity,

I've followed your instructions, and it seemed to go well. I moved what was sitting in C: out of the way (to p), and then changed D: to C:.
Everything seemed to be fine, but on the next reboot, P: had moved back to C:, pushing C: back to D:, and preventing boot.

Whatever is C: now is 100MB - is that the Windows RAM disk I've heard about?

Have attached photo of diskpart view: Image - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting
My System SpecsSystem Spec
28 Jun 2011   #7

Win 7 Ultimate x64

I'm now getting
BOOTMGR is missing
Press Ctrl+Alt+Del to restart
even before all my windows sys files are loaded.

A very fine sheen of sweat is now lightly resting on my brow..!
My System SpecsSystem Spec
28 Jun 2011   #8

Windows 7 Ultimate SP1 64-Bit

I think your problem is being caused by the fact that the System Reserved partition is grabbing drive letter C, which it shouldn't be doing vis my DM screenshot.

Drive prefixes changed by windows - can't boot-dm.png

Once you can remove it, drive letter C will be available for your Windows partition, which is currently D. Also, the System Reserved partition needs to be Active, because that's where the boot record is. If you have your current drive D active that'll be why Windows is complaining it can't find the bootloader.

My System SpecsSystem Spec
28 Jun 2011   #9

Windows 7 Ultimate RTM (Technet)

System Reserved is SUPPOSED to be the boot drive, the active partition, but it should NOT have a drive letter at all.

I can post a screenshot if need be, showing just that.
My System SpecsSystem Spec
28 Jun 2011   #10

Windows 7 Ultimate SP1 64-Bit

Yes, that's my take on the matter. I think I read somewhere you can get rid of the system reserved partition and have C as the active drive with the boot files on it.

Only trouble is, if you do that you lose the ability to invoke a startup repair by use of the F8 key.

Somehow we need to remove the drive letter off the system reserved partition and make that partition active. Once your D drive letter is then changed to C Windows should boot correctly.
My System SpecsSystem Spec

 Drive prefixes changed by windows - can't boot

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