How to Recover a gone OSX (mavericks) on MacBookPro? I shutdown my computer for some reasons with power button (cold shutdown). Unfortunately, my OS i.e.,mavericksis gone at the moment and I have no backup from the Data and settings of that Hard drive partition.
  I have the mavericks installation DVD, and tried to repair the disk with Disk Utility but it didn't work. getting the following message:  


  Disk utility stopped repairing 'Macintosh HD`, Disk utility cant
  repair the disk, back up as many of your files.....'


I have 2 partitions on my hard drive including Macintosh HD which my OS was installed there, and Mac Store that contains my own data.
I tried to reinstall and recover the OS on the same drive i.e,Macintosh HD in order to keep the settings (password, usernames,) and information of my hard drive (However,later I should do the clean install).   To do this, I selected the Macintosh HD disk, and clicked on install , but I am getting an error saying 


  The content of disk can't be changed. OSX couldn't be installed on
  this disk.


So I wanted to ask

1. Is there anyway to get my previous OS to work (I need my passwords and Data in Desktop,documents and download folders)?  

2. Even if 1 is not possible, how can I backup the Data of that partition i.e,Macintosh HD?  

3. Is it possible to extract my saved passwords on Firefox as well?  

Thanks for your help.
Problem has been solved, Just thought it may be useful for others.  

1. Is there anyway to get my previous OS to work (I need my passwords and Data in Desktop,documents and download folders)?   


  Maybe, But I don't know yet. But anyway, it is better to clean install
  the OS again to make your computer faster.


2. Even if 1 is not possible, how can I backup the Data of that partition i.e,Macintosh HD? 


  Yes, basically I installed mavericks on a USB thumb drive. Next I log
  in my new OS and copied everything I needed to a external Hard drive.
  Then I formatted the whole MAC HDD and then clean installed the OS
  there. Now it is working well.


3. Is it possible to extract my saved passwords on Firefox as well? 


  Yes, Once I installed the Mavericks on a thumb drive, I went to user
  folder, library/application support and then found Firefox folder and
  copied my profile . After I inistalled the OS on MAC HDD, I installed
  firefox and then pasted that profile in the same place. All of my
  passwords and bookmarks are there.