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I wanted to run something off of my old Windows XP install, so I plugged it in as an external hard drive and attempted to boot from it. The machine blue screened on me. (I now know this is a bad idea). I then attempted to boot as I normally would from my internal hard drive, which has Windows 7 installed on it. It would not boot. I went through the start up recovery wizard with no luck. I swapped the drives and was able to boot XP. The device manager showed that the disk with windows 7 on it is now exactly the same size as the disk with XP on it (it used to be significantly bigger) and it needed to be formatted. I didn't want to do that, so I tried another avenue. I booted an Acronis disk drive cloning CD with both drives attached. When selecting the Windows 7 disk, Acronis reports that the disk itself is the size of the XP disk but contains volume that is the correct size, which of course is larger than the reported disk size itself. Odd. So I know the volume is still there, but something screwy was probably written to the MBR on the Windows 7 disk when I tried to boot from the other drive. Any ideas how to repair the Windows 7 disk? I'm trying to get it to recognize it's true size and boot properly again without formatting or reinstalling the OS for fear of irreparably losing disk space or data.

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Make the bootable TestDisk cd, boot from it and follow the tutorial, it will not write anything to the drive until you tell it to, otherwise send it in for Logical recovery, I would stop mounting the drive in windows or other OS as it writes to the drive each time, which may overwrite data making that data unrecoverable by anyone.

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Problem solved! I ended up using HDAT2 to restore the capacity of the hard drive. I had originally used the Hard Capacity Restore Tool to do it, but that only brought the capacity up to about half of the desired total.

One trick I had to employ when using HDAT2 worth mentioning: after removing the HPA, I unplugged the hard drive. I found that if I left the hard drive plugged in and rebooted, the capacity would drop back down again.

After the drive was reliably showing its capacity I used the Windows 7 start up repair wizard and I was back up and running in no time.

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