Now, I'm not sure if this first part has anything to do with the problem, but I'll include it here just in case: So, I plugged my external hard drive (which is an internal hard drive that I inserted into a hard drive enclosure) into the USB port on my iMac G5's keyboard. I didn't know at the time that the keyboard usb slots only offer USB 1.1 speeds. I noticed the slowness, so I unplugged the drive, forgetting to eject it first. The mac gave me an error saying sme of the data might be lost, and that I should eject first next time. I plugged it into a windows based machine, and it still mounts fine and all files seem to be there/working. Not sure if this has anything to do with the actual problem. After this, I plugged the external drive into one of the main 2.0 speed USB ports, and the drive just won't mount. I can still mount it with 1.1 speeds, but whenever I try a 2.0 port (tried multiple ports on the Mac) it just doesn't show up. It even shows up in the system profiler, but I can't get to the drive itself. I assume this is a USB high speed driver issue? Where can I get the right files to get this thing to work at decent speeds? Or is it something else? Any help would be greatly appreciated, thanks a lot guys.

I had EXACTLY the same problem with a ViPower enclosure and a Mac mini, but installing the latest OSX update (10.4.4) solved it! I hope it'll help you, too... isa

Try the OS update as stated above. Another thing to see if the machine is seeing the drive but for some reason not mounting it is to navigate to the Macintosh HD- >Applications->Utilities folder and launch the DiskUtility application inside that folder. This will list all the attached drives and if they have directories the OS can read (the second line of text that is indented). If your drive shows up here but there isn't a second line I would copy the data to your windows machine then erase the drive on the windows computer (the reason to do this is that windows formatted drives are readable by both platforms but mac formatted drives are only readable by macintosh computers), copy the data back to the drive and then try connecting it to the iMac again. One other thing to try if you don't want to go to all that trouble first is to create a new user (System Preferences- >Users) then logging in to that user to see what happens while trying to attach the drive then. Good luck!