You are going to have to get a probate judge to accept your account of what happened. The other potential heirs of your father will have a chance to contest your account unless you are the sole heir.
Obviously, if you can afford to do so, you should have lawyer in the probate state represent you.
Usually the POA lapses upon death, so you'll need to be accepted by the Probate Court (and possibly heirs at law if there was no will either) as executor of the estate, then you will have the authority to manage the accounts. If your father meant for you to have the entire estate and you have the documents to prove it, you will have to present this evidence in front of the probate court.
You will need a local attorney to represent the estate, file the appropriate documentation, send out timely notices to heirs and creditors, and make the requisite court appearances. If there was no trust and no will, your state's probate code will determine who the heirs at law are, i.e. the other people legally entitled to your father's estate. Probate courts are courts of equity meaning their goal is to determine the intent of the testator (your father) and carry out his intent. If you can prove with your documentation (and other appropriate evidence if needed) that your father's intent was for you to inherit the entire estate then the court is obligated to carry out his wishes.