I recently purchased a 27 inch iMac and I am unable to get my external hard drives to mount. One is a new seagate and the other is a simpletech that is several years old. Both are NTFS formatted and neither of them show up on desk utility or system profiler. I downloaded Tuxera NTFS-3G but that did not help. Both external hard drives work on my PC laptop and on a friends 24 inch iMac. I know the USB ports work because I have a card reader and a flash drive that work no problem. Anybody have any idea what might be the problem?