1990 ford mustang hatchback?

Just got an old 1990 Ford Mustang hatchback haven't had any issues with it this morning went to go turn it on and it's completely dead is there a reason for this is it because it's cold out this morning because I just had it started two days ago

Get a jump. Car starts, get the battery charged and load tested or simply replace it. No start, call for a tow to a garage.

I'm sure there's a reason but no way anyone here can tell what it is.

If the battery is over 4 years old go buy a new battery with the correct CCA rating for the vehicle.