Check to see if the compressor is running. You can usually hear it, also you should be able to feel it vibrating and it should be warm.

If it is running remove the cover inside the freezer so you can see the evaporator coils.
Check that the freezer fan is running.
If there is no frost or only frost where the freon enters the coils then it is a sealed system problem and probably not worth fixing as you need a pro.

Note: Be sure to check it after the compressor has run for a couple hours. If you check just after a defrost cycle there of course will not be any frost.

From your description of no cooling at all that is what it sounds likea sealed system problem.

But just in case your evaporator coils are clogged solid with ice/frost then you have a defrost problem and that should not be a difficult fix.
A model number would help if this is the case.