Anyone remember which episode this was and what happened?

Mr. Drummond somehow winds up in the hospital and gets amnesia. It ends with Willis and Arnold going to see him and he does not remember them.

I saw this episode a while back and never caught the second part.

It was a two-part episode: "The Accident". They were going to celebrate the 50 birthday of Mr Drummond and a drunk driver crashed with him while he was coming back from the bank. Then when Mr Drummond wakes up he's suffering from amnesia. But he recovers the memory before he looses his business and custody of the three children and they all end up singing Happy Birthday.