You got scorp123's auto reply
He does not like M$
But he is right.
If you can't change from ntfs we must fix the problem
Take a look in /etc/fstab
If your external drive is listed there in ANY way mintDisk will not mount it.
If so back up fstab (sudo cp /etc/fstab /etc/fstab.bak1)
and then open it and delete the entry for this disk (but nothing else) - you need sudo to do that.
Now it should be mounted r/w - if not post back and we'll dig deeper