What to do with arguing parents?

My Mom and Dad were an exemplary couple until the time we found out that Dad had fathered a child during his bachelor days. Things have never been the same since then. Mom and Dad have been quarrelling often and Dad would sometimes leave home and would not return until after several days or sometimes week. I would like to bring back the happy old days in the family. I love my family so much and I could not bear seeing our dreams crumble into pieces just like that. What shall I do?