In a failed attempt to install Linux Mint on an external hard drive, I damaged the disk. Now, it does not show up in the 'My Computer' folder or in Disk Management. I speculate it might have to do something with the fact that i formatted it to EXT3 and it is unreadable by Windows. How can I format the hard drive back to its state if my computer cannot recognize it?
You could boot using a Live Linux disc to fix it. Once booted you could use GParted if you like GUI's or
Important: I am assuming that you did the whole external device and that you want to fully wipe the thing. If that is not the case, then let me know and we can work on that. However, this will wipe the drive of your data. So measure twice, cut once (i.e. double check everything and understand it before blindly typing the above).