Find the disk utilities. (select the blue/light blue square face icon, Select the applications folder, Select the utilities folder)
Select the disk utilities icon.
On the left side, if you have the hard drive plugged in, you should be able to see it there, along with the mac's hard drive. select your hard drive if you see it there and then select repair disk button on the lower right side.after it's finished, it the eject button, unplug then plug it back in.... anything??? I definitely feel your pain.