I have a 2001 Sebring and was parked around 2,5 months in parking,i
didn't drive it..

and it was around -20 somedays( i m in Moscow)

So,i tried to turn on engine but it dosen't work,i tried to do jump start,
car alarm and headlights worked but not engine..

Please help,what to do?

Thanks in advance!

 

There are a number of possibilities. It's not surprising that the battery was dead after the car sat so long in cold temperatures. There are systems in the car that are on at all times (clock, remote keyless entry receiver, alarm) and they will flatten a battery eventually, sooner in cold weather.
If your fuel tank was not full, you may have gotten some condensation that froze, so the car may not be able to move fuel to the engine.
Begin by checking for stored fault codes. If any turn up, make the necessary corrections.