External undetected

I just got a new MBA 13" and wanted to try it out with my trusty Seagate FreeAgent for Mac 1TB external. I normally use it with a FW800>400 cable into my older iMac. I picked up a thunderbolt>FW800 adapter and a FW800>800 cable and was ready to see how some transfers went. Long story short the drive won't mount. Disk Utility can't see it (so I can't format even if I wanted to) and the system profiler sees it as "unknown device" under the thunderbolt port. Am I missing something here? It's always worked (and still does) perfectly fine via the 800>400 cable into my iMac, what gives?