Yes, technically you do.
At the time of your mother's death all of her property of any kind (with the exception of anything with a beneficiary designation) immediately became vested in a legal entity known as her "estate" and that's who owns it now. You can't take possession of it or do anything with it because 1) you don't own it and 2) the estate or the court hasn't given you permission to do anything with it.
You are correct in that a POA ended at her death and can no longer be used for anything.
You would want to visit with a local lawyer that does probate, you can find one at www.lawyers.com, and go over the property that she owned as well as any debts that she owed. There are several different kinds of probate that may apply, depending on the facts. These can range from a simple form you file with the court and then that takes care of everything, all the way up to a full probate which can be long and complicated. The only way to know which one is correct is to sit down with a lawyer.
You don't want to use the wrong one because if you do, then it costs A LOT to correct the problem.
I once was in court when someone came in with a lawyer on a probate matter. Twenty+ years ago they had wanted to save a few hundred dollars and decided to do it themselves and had done it incorrectly. When I saw them they were about halfway through the process of correcting the problems they had caused and had already spent $20k in doing so. It's easier and cheaper to do it right the first time than to correct it later.
If your question has been answered then I'd offer my best wishes to you and ask that you please not forget to leave a Positive Rating so I receive credit for my work. Of course, please feel free to ask any follow-up questions in this thread. I want to be sure that all of your questions are answered.