What can I do for my mentally stable but physically frail parents?

Bonstance, I don't know which is worse. My father is physically fit, but his mental state is depression. He does not want to leave his room, does not want to be around me or my husband. He does not phone anyone including my sister and brother. When he does speak it's to argue with me or my husband. I'm trying very hard to send him to a senior center. I want him to interact with people his age. I wish my father could do what your parents do, he's only 76 years old. He acts like tomorrow is his last day on earth. Meanwhile he has everything to live for, we take care of him pay all the bills. He has no worries but he always finds a way to make himself miserable. Lets hang in there, God Bless us all on this site.