iMac can't see my external hard drive
I plug in a Toshiba 500 Gb External Hard drive and it doesn't show up on the desktop, in the finder window or in Disk Utility. It shows up in all those places on my work iMac and my son's laptop. Any ideas why my computer doesn't recognize it? Thanks for any help.
iMac, Mac OS X (10.7.4), 2.5 GHz Intel Core i5 w/4GB memory