Windows 7 HP - corrupt registry - C: in reg needs to be D: - COA torn

WrinkledCheese · 20 May 2015

Hey All,

Someone asked me to look at their Acer Aspire One netbook without a CD-ROM. It's been a while since I've even looked at Windows so I spent an hour or so the first day and then spent the entire evening. I've tried a "few" things.

Using the built in system repair tools. I loaded up the command prompt and launched regedit. I loaded the System hive and found that all of the paths pointed to C:\ while it seems the Windows installation is on D:\. I tried to use diskpart to activate D:\ as the boot disk, it made no sense but I tried it anyway. Not being familiar with Windows I didn't know if activating another volume would rename the lettering. This resulted in the boot record missing. Using unetbootin and an ISO I found under the couch cushion to load the System Recovery tools. I used this to set the active partition back to C:\ so I can get back to the built in recovery tools.

I've thought about loading up the couch cushion recovery tools so I can copy D:\Windows\System32\config\RegBack\SYSTEM to D:\Windows\System32\config\
I loaded up the backup registry and it seems that it's not going to fix anything as it still points to C:\ instead of D:\. Eg System Root registry entry is C:\Windows but there is no C:\Windows. There is only D:\Windows.

I can think of two options.

Reinstall - The torn COA proves to be a problem here. I can't find out what the registry location is for the product key, nor an algorithm to make it human legible.

Look under the couch for another disk...

I believe I the system has Windows 7 Home Premium 32bit retail. I suspect this because the Software/Microsoft/Windows NT/CurrentVersion/ProductID4 - or something like that - says retail in the product ID. This is the reason I think the disk I have doesn't work. I suspect the couch disk I have is OEM, but I have not bothered to check.

Considering the situation, and pretending the laptop is mine, what would you suggest?

leejosepho · 20 May 2015

First, I believe this (from your thread title) is not actually true: "C: in reg needs to be D:". None of my Win7 installations are actually in/on/at "C:", and yet Windows 7 ignores that and *always* shows itself as running from "C:" anyway. So, going into the registry from the outside and changing "D:" to "C:" would likely only make matters worse for you since your Win7 is likely *not* actually on "C:".

WrinkledCheese said:

...Acer Aspire One netbook without a CD-ROM.

I would use an USB adapter and an optical drive to boot into Win7 recovery mode to see whether it can find a "last known good configuration" to restore.

Anshad Edavana · 20 May 2015

Hi

First of all you should know that drive letters are not static but dynamically assigned by operating system. For a disk, there is no such thing as "C" , "D" etc. A disk will only have a partition table describing the start sector of all partitions and the total number of sectors each partition contains. A MBR partitioned disk can have up to four primary partitions. It's up to Windows to name which partition "C", "D" etc. "Windows Vista and upward versions of Windows are hard coded to name the partition which has OS installed to be called "C". That is even if you install "Windows 7" to the fourth partition of a disk, you will see Windows named it as "C". This is to maintain compatibility with older softwares which may expect Windows partition as "C" and may not work properly if letter is changed.

A normal "Windows 7" setup routine will first create a small 100 MB partition and use it as the "System" partition which contains boot critical files. Actual Windows will be installed in to the second large partition but Windows will name it as "C" instead of "D" because of the reasons i explained earlier. When you boot from a Windows install DVD/USB, you are actually booting a highly stripped down version of Windows called "Windows Pre-installation Environment" aka "WinPE". Since this pseudo OS is running from a DVD and independent from the OS installed on HDD, it will have it's own drive letter assignments. Naturally the first 100 MB partition will be assigned with letter "C" and second one will get letter "D" and so on.

I hope this will clear the confusion about drive letters.

WrinkledCheese · 20 May 2015

Thank you both for the clarifications as to why the Windows registry was referring to C:\ when in fact the files it references could only be found on D:\. It's a behind the scene compatibility layer that is invisible to me.

For clrification, I use Slackware Linux for my own systems so I am quote familiar with the dynamic nature in which "drive letters" are assigned. I also understand the lettering compatibility as I manage mostly FreeBSD at work and there is a designated unix style drive letter for Fat formatted disks. I also run OS X. This is why I'm not familiar with Windows, I haven't really touched it since XP and Server 2003 were the "top dogs" in the Windows world.

The Acer has a 16GB recovery partition, it seems, and I believe I've already tried last known good configuration, as well as every single system restore point that was available. If I remember correctly, Windows creates automatic restore points during updates.

When I checked the ProductID in the registry, it seems that the Acer has a "retail" key, and I believe the ISO I found under the couch cushion is an OEM disk.

If I could get the key from the registry. I found today that there are some Linux tools that will be able to load a Windows Hive file to get the Key from it. It it matches the 2 full banks and 2 partial banks on the COA that are legible, I will try a fresh install.

SIW2 · 20 May 2015

Here: A23x86.iso

Boot it up, then click NT6Repair, which you will see on the desktop.

Select the windows drive letter in the dropdown. Then click FIX.

Windows 7 HP - corrupt registry - C: in reg needs to be D: - COA torn-fix-os-letter.jpg

WrinkledCheese · 20 May 2015

Seeing as how it seems you wrote that software, what exactly does that software do? Specifically, what does the code do that you've instructed I run. Is there any documentation I can read? man page, anything so I can understand what the issue is/was should it fix it.

SIW2 · 20 May 2015

There is a problem with the mounted devices in the system hive. The wrong letter is attached to the device value.

Sir CornBlower · 20 May 2015

SIW2 said:

There is a problem with the mounted devices in the system hive. The wrong letter is attached to the device value.

Just registered simply to convey my gratitude to you sir.
You're a national treasure on this site.
i won't elaborate much further but you've saved my biscuits in more ways than you could imagine.
Thank you.
....(first comment):)

WrinkledCheese · 20 May 2015

SIW2,

Thanks for your live disk. While your instructions didn't resolve my issue, it gave me the ability to replace the last d:\Windows\system32\config\RegBack files that I couldn't with the built in system repair untilities. Once I replaced d:\windows\system32\config\system with d:\windows\system32\config\regback\system

Once I got into the system it's abundantly clear why the registry is corrupt. There are viruses up the wazoo.

I'm running Trend Micro Rescue Disk. I wish I could find my Flacon4 UBCD USB drive.