Have you tried changing the partition?
Start Disk Utility, with the external drive connected and turned on.
Click the line with manufacturer's info, probably has the W-D and the drive size, or the model number. Click the Partition tab, and change the Volume Scheme to 1 Partition, and make sure that Format is set for MacOS Extended (journaled). Finally, click the Apply button, and agree that all data will be deleted.
Does that complete OK that time? If not, what does happen? Any messages or errors?