Clicking sound on an external hard drive is an indication that it's quiting to work. You mentioned that it's just stopped working, you may need to check the Disk Management of your computer to see if you could still reformat it. To do this, please follow the steps below:
FOR WINDOWS XP AND VISTA:
1. Make sure that the HD is properly connected to the computer.
2. Right-click 'My Computer' or 'Computer' folder and then go to "Manage".
3. Locate and click Disk Management.
4. Then, take note of the drive letters that will appear on the screen.
5. While the Disk Management window is opened, unplug the HD and check which drive letter will disappear.
6. If a drive letter disappears, then that is your external 250GB HD. You may reformat it to make it work again.
NOTE: Reformatting the HD will erase all the files saved in it. You may want to bring your HD in any data recovery center to retrieve the important files. If the HD didn't show up under your Disk Management, then there's nothing that we could do but to bring your HD in to the Data Recovery to save the files.
FOR MACINTOSH OSX:
1. Connect your HD to the computer.
2. Click 'Go' (located near the Apple icon, Finder, File, Edit and View).
3. Select Utilities and then click the Disk Utility Icon.
4. Take note the drive letters and then unplug the HD.
If a drive letter disappears, that's your HD. If nothing disappears, then the computer no longer detecting the HD.