External drives won't work since upgrading to Lion.

This is a really frustrating problem. I have two portable external hard drives that have both ceased to work ever since I upgraded to 10.7. These are both used for large video files and I need them to work as they have some important stuff on them.

One is a 1TB WD MyPassport, USB connection.

The other is a 500GB Seagate FreeAgent, FireWire 800 connection.

The drives are both giving me the same weird phenomenon:

I plug them in, and they'll boot up--sometimes right away, sometimes after several minutes--but then they make my Finder worthless. The files won't preview in Cover Flow, and expanding a folder takes forever. When I try opening a video file in QuickTime, I end up with the beach ball of death. I try restarting the computer, but I can't even do that because "Finder (Not Responding)."

So I tried manually shutting down by holding down the power button. When I restarted the computer with the drive attached, the Finder wouldn't launch. The dock would appear, but no icons on my desktop whatsoever. When I unplug the drive, once again hold down the power button to shut down, and restart without the drive attached, everything boots up just fine.

If anyone has experienced this, please help ...