I met my wife 6 weeks after giving birth to our son I say our because I have raised him as my own even though he is not biologically mine. When she did the birth certificate before I met her she left out the father block and left it blank. We got married and we just changed her name to match mine. Can I just put my name in the father block or do I have to get the sperm doner to sign off on this. He is not in the child's life what so ever.

He isn't just the sperm donor; he's the biological father.

Ask him to sign so you can adopt the child, if that is what you want to do.

Your wife may or may not be able to change the birth certificate - what State?

Has there ever been an order of paternity?

The state is virginia and there has been no order of paternity there is no fathers name on the birth certificate

Here is the form which your wife needs to complete and file in order to change the child's name. There is space to explain why she is changing the name. Are you interested in "simply" changing the child's name OR in adopting the child?

Virginia Petition for Change of Name of Minor - Free Legal Form (http://www.ilrg.com/forms/namechange-minor/us/va)