Oh crap what just happened?

[Gongo]

So I use an external HDD 400 gig internal with an external box. All is well and good then suddenly the HDD appears blank and windows asks me to format the drive... did I just lose everything on there?

[xenotype]

I would try to re-seat all the connectors, a different USB port on the computer, and if possible another computer. If all that fails, put it inside a machine, locally, still no-go, i might RMA the drive.