New Hard Drive Enclosure not being detected by Mac

Hi. I've been having problems with my external hard drive. I went out and bought a hard drive enclosure today at Best Buy for more storage on my eMac. After putting it together, I plugged it into my Windows 7 computer to test it out and it worked perfectly, but when I tried to plug it into my Mac computer nothing happened. I went to Disk Utility to check for the drive but nothing appeared. All the USB ports on my computer work great as I have used them all before, but I am unsure as to why it can't detect my drive. I then tried plugging the drive into the USB port in the keyboard and at least got a "USB Low Power Notice". (Better than nothing, right?) This is a relatively old mac computer (2003?) and the software has never been updated because its not connected to the internet and never has been. The USB hard drive enclosure uses USB 3.0 and the hard drive has been formatted to NTFS. Is there anything I can do to get it to work? I can access it and everything on my Windows computer, so why does it not even appear in Disk Utility or the USB Device Tree on my Mac? The manual says that it is compatible with both Mac and PC. Thanks in advance.