During installation I don't know what goes wrong but i corrupted my original boot entry and after installation i was not able to see my original Ubuntu installation on boot entry. And to my horror i was seeing strange grub-rescue prompt.
I thought I lost my previous installation and I will not able to use my new installation as well. but then after searching a while I found following commands using which I was able to boot into my both installation.
If you encounter this prompt then don't panic there are plenty of way out. I just figured out one way. Not a permanent solution but will work till I found permanent solution.
Type "ls" command on "grub rescue" prompt, it will display available partition on and available hard disk on machine.
It will show something like following
grub rescue> ls (hd0) (hd0,1) (hd0,2) (hd0,3)
"Set" command will show you current boot entry, something like following
grub rescue> set prefix=(hd0,1)/boot/grub root=hd0,1To see content inside partition, give following command.grub rescue> ls (hd0,1)/ ./ ../ lost+found/ boot/ sources/ /scripts/ /tools/ /dev proc/ sys/ bin/ etc/ home/ lib/ mnt/ opt/ media/ sbin/ srv/ var/ root/ tmp/ usr/ antarix/ README log/So this way you can be sure if you have lost any data or not. I my case everything was fine.So now I wanted to boot into my installation on hd0. For that i used "insmod" command.insmod /boot/grub/normal.modIt will load grub module in to normal mod, you can press tab twice to see list of available option or type help.And after grub loaded in to normal mode I used "normal" command and my older installation of Ubuntu started to boot.