I have a dual boot (Windows 7/Ubuntu) system and I recently accidentally formatted a 500GB partition on a 1TB hard disc (see thread "Lost Data after formatting hard disc"). I could not recover the original partition but recovered the important files I had lost. Then I tried to format the partition back to how it was originally (500GB NTFS). After my disastrous accidental formatting the 500 GB had broken into about 5 sections - 3 large ones of circa 410 GB, 50 GB and 9 GB and two small ones (MBs). I used GParted but I could not see a way to put the Humpty Dumpty 500 GB back together. I then decided to boot up into Windows and use the Windows utility. I think I could have done it right but I ended up formatting each of the 3 large sections into separate NTFS partitions (More, Spare 1, Spare 2. Extra is the [original, untouched] 500 GB partition on the 1 TB disc). All seemed OK then I rebooted. I never got the chance to select an operating system. Black screen with
Error no such device: 801be6c2-cabc-49f8-a74f-fa06b7167cbf
grub rescue >
I then used Boot-Repair Disk.
Before repairing I saved the report http://paste.ubuntu.com/5645194
Then I repaired (2 or 3 times) but it did not work.
The last report made is http://paste.debian.net/244553
I looked at the latter report and even my dumb brain can see that what I did was stupid (I should have formatted dev/sdc2) but I am surprised that a fault on a disk that does not contain the OS means that the computer will not boot.