Cannot detect external hard disk
I was trying to use my external hard disk today but when I plugged it into the usb hub, my iMac wouldn't detect the hard disk even though the light of the external drive is on.
I checked the disk utility but the hard disk didn't show up.
I have another external hard disk which is always plugged in and used frequently, that works fine and can be seen in disk utility.
Any tips or help would be appreciated, thank you!
iMac, Mac OS X (10.7)