First, let me note that your story proves 2 well-known things:
1. External hard disks aren't suitable for data storage (just for transport and backup)
2. If you have only one copy of data (no backup) you risk to lose it (that's a calculated risk, if the time to make a backup is more than the time to make the documents again).
The first thing to do is to go into Disk Management (that's a part of Windows, use google to find how to do it in your version of Windows - 98, ME, 2000, XP, Vista, 7, 8, you didn't tell) and see what it says about that disk - if it's really broken it will not find it, if it's only unallocated or corrupted it will say so, and that's more info than other parts of Windows, like Explorer, do).
How to proceed depends on what you find.
Just in case it's your computer that gives the problem, not the disk, retry on another PC.
The worst that can happen is a bill of 2000 dollars to recover a large part of your "really important" info. But maybe a new case for the disk (20 dollar) is the solution. Or even a free recovery program.
excuse me..i have a problem about my external hard disk..my hard disk couldn't connect with my pc..i've tried several method where i try to connect many times and also using different usb port in case that is the problem..however, it doesn't work at all..do u have any idea what cause of it and can it be fix..all of my documents,assignment,homework,video,pictures are really important to me and i have no backup..so sad..i hope u can help me..:(