It was previously connected to and run Check disk Repair option. That may bring the MBR's or FAT's to agreement again and allow it to be read.
If that doesn't work there are 2 distinct types of Data Recovery Software available the first type rebuilds the Partition and is generally much faster and more expensive than the type that recovers files individually or by file type.
My first choice would be On Tracks Easy Recovery if you look here are the specifications
http://tinyurl.com/3bzddx
Spin Rite is slightly cheaper and I'm told works well it's here
http://tinyurl.com/8p4ex
Then you have these products available any one of which may suit your needs and hip pocket
http://tinyurl.com/pfuhz
http://tinyurl.com/273ay5
http://tinyurl.com/afu2j
http://tinyurl.com/rmvrv
http://tinyurl.com/yyk8cm
http://tinyurl.com/3t8o3
http://tinyurl.com/fwa22
http://tinyurl.com/382vm
http://tinyurl.com/nc4kx
http://tinyurl.com/70lc
http://tinyurl.com/djw6u
http://tinyurl.com/zsplc
http://tinyurl.com/f73se
http://tinyurl.com/m4w5s
The last one Win Hex should only be used if you know HEX inside out as it's a powerful tool that has the ability to do a lot of damage if used improperly. So don't touch it unless you know what it is that you are doing.
With any Data Recovery if the HDD is having it's partition rebuilt you copy the data off the affected HDD after the Utility has been run but with the ones that recover file or files by type you need to save these to a different HDD to prevent overwriting any existing data so never save anything to the affected drive if you are using this type of Recovery Utility.
You should also consider disposing of this HDD as a Long Term Storage Solution as it is now damaged and isn't reliable any longer and a HDD is much cheaper than the cost of a decent Data Recovery Program or even worse if you need to take the drive to a Date Recovery House.
Also you should keep a full backup of everything so that when this happens again you are not adversely affected. Computer Hardware is worthless without the Data to run on it and that is the most valuable thing on any computer system the stored Data so you need to protect it like it has the value that it actually has.
If you are not careful enough to prevent HDD falling you shouldn't use them as you will kill them in very short order and while it is a fast method of backing up it by no means safe or secure method to use.
Last year I had to rush a HDD through a Recovery House for Tax Information that was only stored on that drive and was needed for an tax audit that cost the company concerned $46,000.00 AU to recover the data off a $120.00 HDD that should never have been used in the first place. In that case the person didn't plug in both USB Plugs and ran the drive underpowered till it died.
If you copy data to DVD/CD you should also be aware that according to Kodak images have a life expectancy of about 4 to 5 years under ideal circumstances so you'll need to repeat the burn to different media more often than that and that only applies to being stored under ideal conditions so if you are not storing them in a Sealed Temp Controlled area I would say re burn them at least once a year if not more often. After all a few Blank DVD are nothing compared to the costs of recovering Data off a dead HDD.
Col