My computer got wiped accidentally due to a fresh Ubuntu installation. Since the drive contains very important data and codes, it would be really great if the same could be recovered.

It is a 2TB hard drive which had Ubuntu 10.10 earlier. It now has a Ubuntu 12.04 installed on it (which I understand occupies ~4GB). The machine has been powered off since.

The installation was done using a usb with the option where the previous ubuntu installation is removed. Since installation doesn't take a lot of time, I'm inclined to think that the disk wasn't completely formatted and that most of the data is still there.

I have no experience with recovery and hence a detailed explanation is very helpful.

NOTE: I can arrange an additional 2TB hard disk for copying data. My computer has a fast internet connection and I have other computers connected to the network which I may use to access the previous one as well.