ANSWER:

Have a look at testdisk which might be able to recover the MBR/partitions on this device. If this does not work anymore try photorec which will attempt to pull of the data of the device by identifying file headers. This is 100% reliable but will also work if crucial parts of the file system were already overwritten.

And oh: Do not perform these tests on the hard disk but instead create an image of it via dd where you can safely experiment on. This way you do not risk to damage the data further in case you decide to hand over the HDD to a professional data recovery company later

by leepfrog from http://superuser.com/questions/423802