I agree with Xpertskir. If it is not cooling, but the compressor is running, then loss of refrigerant is most likely the issue. Depending on the age of your freezer, it will probably cost less to find another one than have someone recharge it (if possible).
Have you tried removing the temp controller, and plug it in directly to an outlet? This way you will know for sure if it will cool. Good luck.
"A fine beer may be judged with only one sip, but it's better to be thoroughly sure." -Czech Proverb