Like I stated, I did correctly unmount the volume. I assumed that the damage must have been caused by grub mounting the volume on boot to look for menu.lst, where it froze, and I did not have the option to unmount correctly. I could be wrong about this however, I just blame grub because of what I saw, however, now I think the problem is actually a hardware issue. I'm sure somebody else knows better than I do, and can possibly help, but I really think its beyond repair now. I have reformatted the drive after saving as much data as I could, which was all the important stuff. However, its still not cooperating. Both my linux machine and my room mate's Mac can read it, linux can write to it, and the Mac can write to it if its formatted as FAT and not NTFS. However, if I try to use it for any length of time, eventually it will give me an Input/output error, and die, only to come back a few seconds later. This happens so fast that Linux detects it before it realizes that it has stopped working resulting in it assigning a new /dev/ entry to it, Thunar automounts it again at a new mount point, and everything I was doing with that drive either fails or does something worse, like copy a whole bunch of data to my system partition in /media.
So, if reformatting it doesn't work, the problem must be hardware, right?
Is it toast, or can it be salvaged? I went to the store today and asked about prices, and they were all way more than I want to spend.

I had the same symptoms a while ago, it was a loose slack joint (is that the right word? that is what my dictionary says for the german word Wackelkontakt) in the power cable, I would check for something like that before dismissing the drive. It may also be worth a try to pull out the disk from the case and connect it to your PC to have a look at it with smartmon-tools or the disks manufacturer's diagnosis tool. May be it is only the case that is failing, those cases are cheap, hard disks are not.

I'm not quite convinced you have a grip on this. I have never seen a 1TB successfully formatted as a FAT drive. FAT has limitations and size is one of them. What are you using to format it? I would use a couple of things First use GParted and see how it goes then plug it into a Windows machine and let Windows format it as NTFS. Don't just do a quick format either do a full format. I have done this a few times where a disk formatted on Linux with GParted wont be seem by something (TV actually) but the same disk reformatted later by Windows is seen.
I think, although this is by no means a certainty, it can be salvaged but look at it his way if you were paying labour/times costs your charge would have already blown out past the price of a new one.

May I suggest you by a new one for your friend and keep working on this one yourself so if you need one you can just use your own from now on. Also turn off automatically booting to USB, although I doubt this was the problem at all.

Then you obviously have never tried it (I have not also, who needs FAT partitions of that size), the maximum volume size for FAT32 is 2TB.

I use FAT on all USB storage devices. It is compatible and it saves space, especially compared to ext*. It's true, for very large HDDs, you may want to use something else.

Wouldn't work for me, since I sometimes have files larger then 4GB, not possible with FAT.

That is a problem, but I don't have many files that big and they can be split.

Didn't think about splitting, but I think it is simply more convenient for to just use ext or (if it has to be shared with Windows) NTFS instead of splitting and re-joining the parts.
But to each his own.

I have actually because I tried to build a multiboot 1TB USB hdd. It failed because FAT couldn't format it. The report was it was to large.

That is strange, may be a limit in the tools used. By the way, how many OSes did you want to put on that disk that you needed 1TB?

A complete set of DebianLive + the full Debian repository for offline updating after installation. I was also going to have Ubuntu (changed my mind on that one) and Linux Mint (also changed my mind on that one).

So I formatted it to ext4, installed Grub and wallah I have a multiboot 1tB hdd with DebianLive and repositories.

I used gparted, I tried NTFS and FAT, both show the same symptoms. I would use ext2/3/4, but since its not my drive, it would be a bit selfish. Also, I still don't have a Windows machine. The drive being seen is not the issue anymore, its input/output errors, which AFAIK are hardware issues.
The disk came as a whole unit, not an enclosure and a hard drive, I can't even find any screws on the thing. Its powered solely by the USB, there is not separate power supply. The cable uses some crazy non-standard connector on the hdd side, so I can't even replace that.

My time is pretty cheap right now, until class starts up again. I'm sure working to fix it isn't going to cost me more then the prices I saw at the store. I'm not going to spend more than $100 USD for 1tb, and the prices I saw here were more than double that.

I use USB boot sometimes. I have a hard drive dock that I use to boot from other SATA drives that I have lying around. disabling it would be a an inconvenience. I also agree now that it probably wasn't the issue, since GRUB should mount it as read only and never ever try to write to it.

If you want to choose at boot time from which drive type to boot only a single key press is necessary, F8 for ASUS, F9 for Biostar and some Dell laptops, F11 for MSI and ASRock, F12 for Gigabyte, Escape for Foxconn. Not very inconvenient, but of course that is up to you.

Only a single key press MAY be necessary, depending on your bios. My machine is a system76 pangolin (p6 or p8 I think), and I don't think I have that option. I have to go into the setup screen and arrange my boot order.

Sorry I thought I read that you said you had access to a Windows machine. It was in Chinese and the person who owned it wasn't as computer savvy as you are. I must have made a mistake as it is obvious you don't have access to any Windows machines.
So in order to limit inconvenience sometimes you prefer to possibly wreck a piece of hardware that isn't yours. Way to go.
Correct, Grub won't do any damage but hard shutdowns like you obviously did can.

Anyway I can't think of anything else that is easy to eliminate, and your not following all suggestions anyway, so good luck I hope you can fix it, or at least replace it.