My Book Essential 3TB USB2.0 Connection - not visible after reboot?

Just plugged in a new 3TB essential drive to my imac and when I do a reboot there is no 3TB drive available any longer? my 1.5TB essential is there but no 3TB. If I unplug/replug the usb then it appears. I have the latest firmware according to WD Smartware. :angry:

Any ideas?

Try a USB 2.0 cable. Macs have known issues with USB 3.0 devices due to lack of support from Apple in favor of Thunderbolt.

Tried that - same behavoir, on mac and pc :cry: