When there is no will (or no executors are named in the will, or the executors have died), the official form is called 'letters of administration.'
In these cases where there is no will, you must apply for letters of administration, which serve the same purpose as probate. You apply for a grant of letters of administration in the same way you would apply for probate. However, as with probate, you may not have to apply for letters of administration if the person's estate was not worth very much.