My Book Essential won't boot

The 3 terabyte USB 3 my book essential is not recognized on the desktop. In disk utilities it will show up if I unplug it and then plug it in again. If I try to repair it it says disk not repairable and recover files. From disk utilities when trying to mount the drive disappears. Drive just spins when on.

What to do?

Thanks

HI there, what version of Mac OS do you run?

Running 10.6.6 but I sent the drive off to ESS for data recovery.

Thanks,

T