I want to ask is there sanbox exist or not. If exist then what are effect of this and waht is solutionof this problem.
You cannot deny the fact that it doesnot exist, yes it does. I have seen by myself, which happened to my own 5-6 sites among the 1000s of stock I have currently. Firstly you have to right away stop doing what you were doing for the last 15-20 days for your site, soon after it goes in sandbox. Have a check on all the things you did since one month back and rectify those things. There might be some bad or sandboxed site where your link might be placed which eventually affected your site, or some other reason.