Hello,
I try to start my server but its not booting my OS . I am able to access grub but when i type boot there its asking me to load kernel first . Anyone can help me bring my OS back up ?

It's not likely anyone will be able to help with the minimal information you posted.

There are over 500 different Linux distributions, which one are you using?
Is this a new install and you have not been able to get it to boot?
Was it previously booting and now will not boot, and if that's the case were any changes made immediately prior to this failure?
Do you still have the medium you used to install your Linux distribution?
Can you boot that?

Hello Yancek,
its Centos 7 and it was working very well on server . I am using the server to host a website but last night suddenly stop . I am not very familiar with Linux OS . So since then i am trying to boot the OS back .
Is this a new install and you have not been able to get it to boot? NO
Was it previously booting and now will not boot ( YES ) , and if that's the case were any changes made immediately prior to this failure? NO
Do you still have the medium you used to install your Linux distribution? YES I DO
Can you boot that? YES i can boot that

I'm not familiar with CentOS and don't run any servers so doubt I will be much help. One thing you could do to get more info which may be enough for someone else to help you is get the bootinfoscript, download it and run it. Just do a google for "bootinfoscript" and you should get to the site. Instructions are on the site and you can post the output her, a results.txt file.