It sounds like the external drive is in a format that the TV won’t accept.
Is the drive NTFS? Does the TV expect FAT32?
If it’s not a formatting issue, the issue could also be the drive itself.
The Smartware-equipped, password-capable externals have had a habit of not playing nicely with many consumer electronics. They work fine with PCs and Laptops and WD’s media players, but things like XBOXes and PS3s and TVs tend to not see the drive at all due to the hidden partition for all the password-protection bits and pieces.
A bare drive like an Elements, should work fine, as long as its a format the TV can understand… other externals are somewhat hit-and-miss.
Then, the other issue is large drives. If the drive is 2TB or larger, it may be incompatible with the TV, even if all else is right. Drives over 2TB need GPT formatting, and many devices don’t understand the new style of partition table.