My 2003 Mercury Mountaineer Won't Start?

It had to be jumped yesterday but started and ran fine after that not a problem until this mornin it was really cold last night so we thought the cold zapped the battery but we tried to jump it wouldn't jump then we went and bought a new battery cause the other one was too small. Had it charged and it still won't start the radio and everything comes on but it won't start. it makes one click noise when u try to turn it over. but it won't start any ideas. It started everytime yesterday after the jump with no problem at all.