Cannot see my external hard drive

Greeting every one.

When I usually plug in my external hard drive, Windows detects that there is a new hardware that has been connected and install its driver successfully. However, when I open my computer, I don't see that my external hard drive is there. No icon, nothing at all shows that I can open while it's working.

I tried to connect the external hard drive to windows XP, Vista, and 7 but it's the same. I couldn't see my external hard drive.

Please Help

Karrar

Yes, there is a lot of data on the hard drive.

First I did everything with the command prompt and it was not detected.

Then I downloaded the testdisk application and it was not recongnized.

Thanks for your follow up and I'm waiting for other options.

I wrote in the beginning that I tried it in different OS and PCs.

So I tested it on XP on different PC, then on Vista on different PC, finally on 7 on different PC.

Best Regards,
Karrar