thankz guys, @default u r exactly at the point where i am looking for. I am doing my second consecuetive masters, the only different is i have used my opt . my intl advisor says tht i m fine n can travel once i get an I-20 n i m waiting for new I-2o to be issued since there is date concern to issue a new one, but i did not find any body having similar experience so the probality that they might stop is high i guess if i travel without taking a sem. of class. But i know there is a rule that since you have a valid visa , you can enter usa  with an valid i-20 within 150 days since u left usa. But u never knows that nowadays port rules and restricitons applied soo waywardly.