I have a 320 gb acclaim portable hard drive. My mac doesn't read it, the first time I plugged it the lap asked me if I wished to format it and I said yes. Now it doesn't read it, what can I

SOURCE: portable hard drive won't show on desktop

it could be defective cause you might have taken the stick off while it was loading or if not you can plug it again and try opening it through My computer/ Removable disk:

SOURCE: verbatim 160 GB portable hard drive doesnt want to open IbookG4

first of all, if you don't have any info there, you should format it, always that helps a lot, but if you have some info and you don't want to format it, well, check it on a pc, if it opens, that means that the hd is fine and the problem is the connection, like renx said, check if you can plug it with firewire, or usb, for mac is recomended the firewire, and its faster, but if you have only usb, it should work fine, so check if you can see it on the desktop, and if not check the finder, maybe it has another name or change its position

SOURCE: I recently bought a Verbatim Portable Hard Drive

ur computer need to be upgraded for that

SOURCE: Verbatim portable hard drive not recognized by XP - works in 2000

Try it is different USB port of your PC. It worked for me.
Farhan

SOURCE: USB portable Verbatim Acclaim 320gb

the power requirements of the hard drive are too much to run it from the laptop, remove any other usb devices and you will find that it works