Since you just bought it, why don't you exchange it? If you have a store nearby, just drop in and swap the one that's not working for a new one. You're within your return period.
If you don't have store nearby, order a new one and return the non-working one.
thanks for replying to my query.i sorted the problem out myself by hit and trial method.kept on pressing power and home button in random order until the tablet started and went to factory reset mode.i kept the tablet on charging.then clicked on power button after that holded the home button and power button both simultaneously.that's how I forced started my tab.(for any user experiencing the same problem as me)
it's working fine now.the only thing i don't understand is why when i put the tablet on charging in the beginning it didn't powered up by itself.it is doing that now.