The first thing is to determine if the compressor is actually on.
You can usually hear it but also should be able to feel it vibrating.

If it is on and there is no frost on the evaporator/freezer coils then it is a sealed system problem.

This will be an expensive repair as you need a pro.
Often it makes more sense to put those dollars towards a new unit.

[COLOR="Blue"]but only in the freezer compartment there is no air blowing in the fridge compartment. Is that normal?[/COLOR]
Not sure about this but it really does not matter as the freezer air is warm.

[COLOR="Blue"]How does the fridge get cold?[/COLOR]
The compressor runs, it compresses the freon.
The freon then travels to the evaporator coils in the freezer.
there is is allowed to expand.
When it expands it absorbs heat.
This is what cools down the evaporator coils in the freezer.
The evaporator fan then pulls air through the coils to cool it down.
This cold air is also circulated into the fresh food compartment to cool it down.

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Could the thermostat be bad?[/COLOR]
No because the compressor is on therefore the unit knows that it is too warm and is trying to cool the unit down.
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Or the defrost timer?[/COLOR]
No.If the compressor is running and there is no frost on the evaporator coils then the defrost timer does not have any effect.

The key here is that if the compressor is running it should cool down some.
Even with a defrost problem where the coils are clogged solid with ice/frost the evaporator fan would blow cool air just not cold enough to get the freezer down to around 3 degrees F.
But it sounds like you have no cooling at all and that is a sealed system problem.