Windows appears to have wiped my HDD on driver install

It's difficult to see how anything could have happened to the drive... the power was off. Surely there must be something else going on?

I just thought of something. I'm wondering if the drive has a compatibility issue with Win 7? I have a brand new Maxtor Black Armor USB drive that did the same thing right after I upgraded to Seven, but works fine on Vista and XP. I wonder if there's a driver or firmware update available? It's something to consider.

It's a WD, so maybe they've made something for it. They usually tend to be on the ball with drivers. Maxtor's website basically says "Oh well, it isn't supported. Buy a new drive." Sure, but it won't be a Maxtor next time.

Do I understand correctly: you have two HDDs, one internal and one external. You installed Windows to the internal while the external was off and you are suggesting that the external, while off, was wiped while Windows installed on the internal - do I have this correctly stated?

If so, I dare say your scenario is impossible.

Monk