External HDD no longer visible?

I am currently running a 500GB Seagate FreeAgent Pro external HDD, and i was looking in my BIOS earlyer today and under boot it said something like boot prioritys for my HDD's. I went into this and it said my external drive was secondary boot priority, i accidentally disabled it under this option and now it no longer comes up in Vista (im using Ultimate SP1 btw) and the option where i disabled it in my Bios has now vanished?? I have looked in my device manager and when the external is plugged in it comes up with a unkown disk drive called disk drive, but it is not visible anywhere else. Someone Pleease help me.

Here is some extra info just in case:

My mobo is P5K Premium latest Bios revison and im running my external through eSATA but i have also tried it with firewire and USB.