Minor issues with an external hard drive

[gold_finger]

If I try to mount the external drive now I get the following error: Error mounting: mount exited with exit code 1: helper failed with:
mount: according to mtab, /dev/sdb1 is already mounted on /home/jonathan/ntfsfiles
mount failed

Error message says it's already mounted -- at /home/jonathan/ntfsfiles.  So, I'm assuming you followed instructions from Help Manual and created an entry in /etc/fstab to automount on boot.  (That looks like what is indeed happening.)  If you go to your home directory there should be a folder called "ntfsfiles".  That's the location now for your drive and the files on it.

Before, without modifying the fstab file, the drive would open Thunar after boot, when the drive would suddenly be mounted.

Now that you have it automounted as part of the filesystem it won't do that anymore.  Just open file manager and navigate to the "ntfsfiles" directory under /home/jonathan.  I don't use Krusader, (looks similar to Midnight Commander and/or Ranger which I have), but that should work fine also -- just navigate to /home/jonathan/ntfsfiles.

If your files don't show up there for some reason, post back the output of these two commands:

Code:

sudo blkid

Code:

cat /etc/fstab

The NTLDR error persists on attempts to restart.

Not sure what that is, but sounds like something left over from a Windows system.  Did you have Windows installed to that external drive at some point?