Recently I installed Ubuntu 14 on my Toshiba laptop overriding windows 8 and ubuntu 10 which was already in it. Only after the installation I realized that this particular option has deleted the earlier partitions and formatted the entire hard drive. I thought 'erase disk' option will format only the os installed drives. Anyhow my last four years work has been lost now :( Is there any way by which I could possibly retrieve the lost data? (it amounts up to 200 GB). Kindly help me. Is it advisable to consult data recovery firms?
First of all I'm very sorry to hear that you've lost all your data in this sudden move, I've experienced the same issue with my laptop, and from what I could tell you can use some of the available recovery tools in the software center,
I would recommended system rescue CD you can run it using CD or a USB flash good thing it is support most of the known partition format.
You can also use Testdisk. It works within the terminal you can run this command to install it
sudo apt-get install testdisk
you can also dig into google and make some search for the same problem and you will definitely find the tools you like, I hope you can recover it soon.
This method is not necessarily useful, but you can try it. I used the bitwar data recovery software to successfully recover formatted SD cards, you can try.