Blocked nose can be caused by deviations in the cartilage or bone which separates the two sides of your nose. This is known as your nasal septum. Sometimes there is no explanation why you have a twist in your nasal septum although it can be caused by trauma.
If your only symptom is nasal blockage and you have a twisted nasal septum there is a high probability that your breathing would improve by correcting the twist in the septum of your nose.