Saw a film on TV some 40 years ago. Black and white. A family man , I think he worked in a bank or financial inst. Was beaten up and robbed and suffered memory loss . Wandered around for years . His son became a brilliant pianist . Ended with him looking through front window of his old home and family around christmas tree.

I believe you are thinking of "It's A Wonderful Life"... classic holiday film starring Jimmy Stewart... :)

Might be The Way of All Flesh (http://www.tcm.com/tcmdb/title.jsp?stid=95176), his son is a famous violinist though.