has a problem w/ ac blower system.

What is your question?

ac fan blower works & blows real good & cold as it should, but very little air coming out vents,can even hear it blow strong.been told that a filter may be stop up ,but can't find it,also been told ductwork may have come loose & fell down.what else can it be & what do I need to do to fix problem???problem happens every time blower is turned on for ac,heat,or defrost.