I have an external hard drive that I transferred a lot of music onto from an old Apple computer. When I plug it into ubuntu it never shows up.
I tried looking through the filesystem for it but didnt really see or recognize anything.
If you copied the files onto the hard drive using Mac OS X, it is possible that the file system is HFS+. Linux doesn't support journaling on HFS+ so Ubuntu will not mount it automatically. Searching the Internet, I see that there are ways of disabling the journaling so that Ubuntu can mount it but I cannot recommend doing this as the solutions appear to me as dangerous hacks. In my opinion the best solution is to find a friend with an Apple computer and copy the files over the network.
To check what filesystem the hard drive is, run the following command after plugging it in:
sudo fdisk -l
You could also use a mac with as much free space as you have used on the drive to reformat the drive. That is, move everything onto that mac, use something like Disk Utility to reformat the drive as ext4 or something, and then move everything back onto it. This would be slow and would require 2N space, but would definitely work.