I was in prison when a default judgement was rendered against me for damages from a car accident, what can I do?

You need to retain counsel and file a Civil Rule 60(B) motion to set aside the default judgment. The better question is whether the default judgment is collectible against you -- in other words, do you have assets that could be seized to pay the other person?  A Chapter 7 bankruptcy may also be a viable option. IMO, you need to sit down with a civil litigator and discuss your options.