Which programs have you used to try to open them? sometimes a different program will have no probs.
Do the Thumbnails view show ok? Or it may even be an 'ownership' problem and you have to take ownership of the files on the ext HDD
Hands-on: Acer Predator Triton 700 review
D&AD Awards 2017: see the best design, advertising, illustration, animation and VR of the past year
How to lose weight with an Apple Watch
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.