My hard drive has all my saved game data but when I play terraria it won't load my saved games
Well, as a simple answer..
Make sure you sign in to the same profile you created the accounts with.
Also, make sure you've selected the hard drive as the storage device.
Worst case cenareo, your hard drive could either be damaged or have a bad connection at some point..
If you don't have too much on it, you can consider getting an external hard drive (SSD) and plugging it into the proper slot.
It's not hard.. look at YouTube for help.
Otherwise, you might have to carefully go in and try to mess with the hard drive. I don't recommend it.. as it can go south pretty quick if you don't know what you're doing.
Good luck with your problem.
I can't really say anymore than that.