Car won't start even gave it a boost?

[Karan]

So I left my car in the parking lot an took the train to school low an behild two hours later came back did not start not even a light or anything. A few hours later my dad got home we went there an tried to give my car a 97 Altima with his 02 Cavalier, we waited an everything almost 45mins an still nothing....is it because the cold it won't start or is the battery just done? it is very very very cold an like I said this morning the car drove fine