I've connected my 320gb prestige usb 2.0 portable hard drive to my computer, so now how do i transfer my file on to it?

i think ther is some bad sector tray to use this prog to test your hard disk http://hdd-regenerator.en.softonic.com/

Try a different usb port on the computer. Maybe the usb port you are using is bad.

Try the portable drive on another computer and see if it is recognized. If not, the portable drive might be defective.

When you plug the drive into the computer does windows alert you that a new device was detected? If you open my computer you should see and hard drive listed that will only be there when your external drive is connected.

one is for data transfer between computer and hard drive the other is a power cable if they are both usb connect both usb plugs into usb ports

plug it into the computer when the drive shows up in my computer assuming your using windows right click on it and select format keep the default settings and hit ok to the format

check cable connection, maybe it didn't connect properly

First try connecting this USB drive to a different computer.
If this did not work then the USB adapter case is faulty, then remove the hard drive from the case and attach the hard drive to an USB hard drive adapter then plug it into a working computer's US port. If the hard drive is OK then the computer will see this as an external storage device and you can open the folders and files to backup the data off this hard drive.
If this does not work then there are companies that can recovery data from faulty hard drives BUT it will cost you an arm and a leg for their services.

Does the Iomega show up under 'my computer'?
It should be another drive (D, E, F whatever) and as such you put stuff on to it the same way you would put stuff on to your C drive.

Does the drive show in Device Manager? Right click on 'My Computer' and select properties, the open device manager.. Navigate down to Disk Drives or Hard Drives, click on the plus sign and see if your drive is listed. If it is, then right click on the drive name and open properties for the drive. Click on the 'Volumes' tab and hit the 'Populate Button'. It may be the disk just needs initialising, then reformatting before you can use it. If it does need initializing, a wizard should appear to guide you through the process!
If this doesn't solve your problem, try using a different USB cable and/or USB ports on your computer, and ensure to unplug all other USB devices other than keyboard & mouse.