Replace engine now will not start

What does it do when you turn the key? Nothing? Clicks but does not crank over? Cranks over but does not start? What do the headlights do when you try to start it? Do they come on bright and dim while you turn the key? Do not come on at all?

Okay, then you need to do some testing to determine if you lost spark or fuel pressure. A quick way to check is to spray a bit of starting fluid into the engine and see if it tries to run. If it tries to run then it is likely a fuel related problem, either the pump failed or it is not getting power.
I would also contact whoever did the engine replacement, this should be something they would take care of, but being the holiday season that might take a while.

Well that's good and bad.

You mean the cooling fan correct? That won't turn on with engine heat until it gets up to 230 degrees F. To test that you need to be able to watch the actual temperatures the computer sees. That requires a scan tool to monitor the temperature from the sensor.

If you can verify the coolant temperature and then see that the fan isn't working there are more tests that can be done, but testing without knowing if the temperature is even hot enough is sort of a waste of time.