The defendant needs to file an answer to the complaint. A defendant may also file a motion to dismiss based on what was pleaded in the complaint. If the motion is overruled however, the defendant must answer the complaint.
There is a difference between defaulting on the repayment obligation, and a default judgment. The defendant still has a right to dispute the debt, though it may seem clear cut to some. But he must assert his defenses, and dispute any facts in the complaint, in an answer.
If you (or someone you know) are/is the Defendant, I'd advise you to speak with an attorney. A general civil or debtor/bankruptcy attorney may be able help you or the person you know reach a solution to the issues named in the complaint.
Disclaimer: This does not constitute legal advice. No attorney-client relationship has been formed through this answer.
In response to a Complaint, a defendant must file a "Answer" (not a motion, with certain exceptions). It sounds like you would have defenses and counterclaims to raise along with the Answer. You should consult with an attorney to do this properly.