Here is my problem. I have Windows 7 and Linux Boss installed on to my laptop. I basically do not have much knowledge about computers. My computer's hard disk size is 320 GB. When I work on Windows, i found 100 GB is unoccupied and therefore i went for partition and added a new local disk E: . But later I came to know that my Linux OS has that 100 GB of memory. Now, I'm not able to boot in to my system as I'm getting error: unknown filesystem. Entering rescue mode... grub rescue> What am I supposed to do to get back both the OSs? Waiting for a positive reply!

Are you not able to boot the laptop? to either windows? or Linux?
How did you install Linux BOSS? CD/DVD/flash drive?

If you can boot from whatever installation media you used to install Linux BOSS, do that and go to the site below and download and run the bootinfoscript. Post the results.txt file it produces. It would seem to be an error in your bootloader installation/configuration.

That sounds like you reformatted (in Win7) what was the Linux partition. If so, you have no way of recovering it without a fresh install of that Linux.
If you have a Win7 install CD/DVD you can recover its boot-loader by using Fixmbr as described on this Microsoft page. That will allow you to boot Win7, but you will have to re-install Linux separately.

Aha. Here comes the main problem. I got my laptop free from the government where the OSs were already installed and they didn't provide me with any installation CD/DVD. And yes, I'm not able to get into the selection screen where it will provide me with the two options to get into the respective OS.

I have a blog post where is described how you can fix your problem: http://www.linuxquestions.org/questi...rtitions-4060/