Can I file a case on the person according to cyber law if some one blocks website ? For example :- my name is srinivasg and I want to open a site with the name srinivasg.com but if some one has already openend the website with the same name srinivasg.com can I file a case being srinivasg

You can file a case against anyone you wish, whether you'll win or not is another matter.

To answer you question better, unless the other party is using "your" name in an anti-competitive, harassing/abusive manner or copyright infringement you really have NO case.
So, someone registered "your" name before you, that's how things are.

BTW there is NO such thing as Cyber Law.

Too add to what Ben said, you are not the only person with that name. First come, first served.

ICANN, the agency that oversees domain naming, does have a process whereby trademarked or celebrity names can get a previously registered domain assigned to them. For example, I believe Sandra Bullock was able to get sandrabullock.com assigned to her from a speculator who had registered it. But, you would have to prove the name was trademarked or copyrighted or that the name is recognizable to you. If there was another person with the name Sandra Bullock and that person had registered the name, she may not have won.

So, if you think you can prove you deserve the domain name, then contact ICANN about recovering it. Otherwise, its is first come, first served. Check out nissan.com