I had Windows 7 installed on a 500GB hard drive. I wanted to install Ubuntu on a16GB pendrive and use it as a hard drive. I made an Ubuntu bootable pendrive on a 4GB pendrive.

Then I booted my system from the Ubuntu 4GB pendrive. I inserted a 16GB pendrive to install Ubuntu on it. I choose the "Something else" option while installing Ubuntu. During the partition allocation and that process I deleted my 500GB hard drive (i.e. /sda) instead of selecting my 16GB pendrive. I came to know about this mistake when I tried to restart my system. It showed this message: Insert bootable disk.

Once again I booted my laptop with the 4GB Ubuntu bootable pendrive. In Disk Utility I saw that my 500GB hard drive has free space.

I have very important data on it. Please help me. It's very urgent.