Lion & External hard drive problem.

Hi, I upgraded to lion a week or so ago and have been fighting with it because I can't get it to recognise one of my external hard drives.
I have two:
1) was an old 2.5" laptop hdd in an enclosure which I used to store video files
2) was an old 1tb 3.5" desktop hdd in an enclosure which I used as a time machine backup of my iMacs internal drive and other external drive.

The 2.5" drive is fine, works perfectly like it did before in snow leopard. But the larger tme machine drive isn't to be seen anywhere! Any ideas?

Kind regards.

The enclosure could be bad. External enclosures can fail unexpectedly. Try removing the drive from the enclosure and reseat it to see if you can bring it back up.

I've already tried that and it doesn't work. It seemed a bit strange that it was working before I upgraded to lion and now all of a sudden it's packed up. Hmmm