Boot up with the Windows 7 DVD. Select the language and click Next. In the lower right corner, click Repair your computer (instead of the giant Install Now button in the middle of the screen).
Choose the Windows installation, click on an Administrative user, then OK. You'll see the Command Prompt as the last or second to last option. Click that.
Type bootrec /fixmbr and press Enter. Then type x:\boot\bootsect /nt60 all /force, replacing x: with the DVD drive detected, then press Enter. Then type bootrec /rebuildbcd and press Enter. Assuming it finds the Windows installation, you're off to the races
It is unknown because you have entered an undefined partition type GUID.
What you have entered:
C12A7328-F81F-11D2-BA4B-00A0C93EC930
While the correct type GUID for EFI System partition is:
C12A7328-F81F-11D2-BA4B-00A0C93EC93B
(0 vs B at the end)
In any case, you should use the following type GUID:
EBD0A0A2-B9E5-4433-87C0-68B6B72699C7
which is Basic data partition in Microsoft Windows.
Since your disk is a GPT disk, you must use UEFI boot. There is no boot code from Windows that is capable of legacy booting a Windows installation on a GPT disk.
For UEFI boot, bootsect and bootrec is pretty much useless (except MAYBE bootrec /rebuildbcd), since UEFI boot is purely file-based (EFI binaries/executables), while bootsect/bootrec only deals with boot code on the MBR/boot sector.
If bootrec /rebuildbcd still doesn't help after you revert Partition 3 to Basic data partition, then you may consider bcdboot. You MIGHT want to delete \EFI\Microsoft under the ESP (Partition 1) first after you mount it with mountvol drive: /s (where drive: can be any available drive letter), or simply reformat it (FAT32) if it's not shared with Ubuntu or so. Then, run:
bcdboot X:\Windows
where X: is the drive letter of Partition 3 under the current environment (so check with diskpart or so first).
P.S. There is a high chance that the actual installation (on Partition 3) is broken or messed up. I suppose how to fix that depends on what error you see when you boot it (after you reinstall Windows Boot Manager and build a new BCD store with bcdboot X:\Windows from it).
Best Answer
sfdiskshould be able to "fix" this problem easily; something like this should "work":However, it's possible that in addition to the partition type being changed, the partition positions (start, end) were also corrupted. TestDisk should detect these issues and write a new, somewhat proper partition table.
The thing is that considering the partition table was corrupted, it's possible, no, likely that the data is too.