Welcome to the community, baxhase!
Do you get any errors when trying to access your files? I'd recommend you to try the external HDD on another computer and see if you'd be able to access it from there. Another thing you should do is go to Disk Management and check how the hard drive is recognized there. I'd also try changing the drive letter assignment again, just to see if that will let you open the files stored on it. You can refer to
this tutorial for the step-by-steps.
Hope it helps. Keep me posted!

SuperSoph_WD