Originally Posted by shyammohan
I have already installed centos6 and win7 on my 350gb hard disk. Two os's were working fine. then i deleted one windows partition via centos. After that there was some problem with the grub.
i found some grub commands from the internet and almost fixed. Right now my windows7 is working fine, but centos6 is not booting.
Your post isn't detailed enough. Without knowing what the problem with grub was and which commands you found and applied we will only be able to give you some general advise.
When you want to dual boot Windows and Linux, you first install Windows and then Linux. You need to do this to make sure that the bootloader (grub from Linux) can handle both Windows and Linux.
You mention that Windows is working at the moment, which makes me believe that you found a way to restore the Windows bootloader (which will not pick up Linux).
You might be able to use the CentOS cd/dvd to restore grub, but like I said before: Without knowing what it is you did this is just a guess.
This link might be of help (general concept): Fix a dual boot Windows Vista and Linux problem
blindly copy/paste the commands in the given link. Make sure you understand what is being done and when in doubt ask!