How to recover data from an external, unrecognized hdd?

Here are a few questions that might help you get an answer.

1. What model of hard drive is it?
2. What is the name of the device when it shows up in device manager?
3. Did this problem just start happening? Did you drop the hard drive? Did you re-install Windows recently?

A few things you can try in the meantime:

1. In device manager, right click on the device and select uninstall. Then, remove the device and reboot the computer. When it's started up again, plug it in and see if it works.
2. Try the drive on someone else's computer, just to be certain the problem is with the drive and not your computer.
3. Disassemble the external hard drive and plug the bare drive into your computer (if you have a desktop). Or get an empty external enclosure and install the drive into that if you have a laptop.

If it doesn't appear as a device in the Device Manager section then it's a problem, the drive might be physically damaged. But if it appeared but said "drive unusable" or some other *** then you can restore your files. What I usually do when I'm in such situation is make a Live Ubuntu USB and boot out of it, browse to your computer and see if you can see the drive from there, Linux based OSs handle drives much better than Windows.

You can take a chance with windows hard drive recovery freeware from http://freeware-fix.blogspot.com/2013/02/external-drive...
It successfully helped to recover inaccessible data from an inaccessible WD flash drive. So I truest it will recover your data back, too.
After this trouble, you should learn to back up all your important data regularly, at least once a week.

yeah! you can recover your all the files and photos. First u want ask you did you try any data recovery software till now? If not try it you will get back your data. And still you won't be able to recover the data then you need to take assistance from a professional data recovery company.