Try things in this USB FW Quick assist faq.
Personally my experience with WD EXT. drives is terrible. I'll never buy again. They don't play nice with Macs, my opinion and others here, and stop working after a short time.
The drive inside is good....it's just the rest of it that doesn't cut it.
DALEMac OS X (10.7.5), MacPro '07 MacBookPro Late '08G4
Thanks for the feedback! Yes, I am a big believer in Disk Warrior's repair program and recommend it to many here. I use DW once a month to try and catch errors in my system from getting too far out of hand. It has repaired every little and big issue I have ever had with my three Macs.