Recover Damaged disk (vdi)

[KCBDurfee]

I am using VirtualBox ver 4.3.26 on Win 8.1, Ubuntu 14.04.2 guest. Recently, I stopped the VM, then on attempted login, I got an error from Ubuntu black screen (sorry, did not copy the exact error, but it was something hinting that my boot sector was not found). I tried re-installing Ubuntu over this but it hangs on step backing up installed packages (I stopped it after 12 hours!). I have a recent backup (vdi) that I installed into VirtualBox and it runs fine, but there are several files I would like to recover from the damaged version. I have tried to add it as a second SATA drive in the Storage options of VB, but I just get an error that drive C: already exists. Maybe it is naive of me to think that i can recover files from this damaged file if I mount it as non-bootable drive, but so far my attempts have failed. Can I do this? If so, are there step-by-step instructions for how? The documentation somewhat suggests I can, but its descriptions do not match my screens as I go through steps to add a second SATA drive.

[socratis]

I have a recent backup (vdi) that I installed into VirtualBox and it runs fine

Well, in that guest that is working, go to VM Settings, Storage. Select your HD controller (SATA? IDE?) and click on the HD with the green plus icon. Select 'Choose existing disk' and choose your damaged VDI. Boot your working guest and the damaged VDI should appear as a second HD.

[KCBDurfee]

Found a solution that worked for me (do not guarrantee this will work every time). I found an ubuntu utility called boot-repair, link and instructions in the ubuntu community web site under boot-repair (google it, I guess I cant post URLs yet...)
I created a new VirtualBox with my corrupted .vdi file, then edit the storage options to add a ubuntu install CD image to the Controller:IDE. That boots to an ubuntu install disk, where you can run the boot-repair program following instructions. Then remove the ubuntu CD image and boot.

[socratis]

Nice of you to let us know about the solution. It may help someone else down the road. Glad you sorted it out.

[loukingjr]

Just to clarify something. Boot-Repair is not Ubuntu or even Linux specific. Boot-Repair