Anything could have happen such a slow voltage. What you need to do is read the display, the display will tell you to press enter to reset the display. Once you have done that the beeping will go away and you can start over. This has happen to my wife several times and she will get very frustrated and walk away. I will reset the unit by pressing the enter button and tell her to start over everything works normal than.
2016 34RL CC; 2008 Ram Mega Cab 2500HD, 6.7L, 68RFE 6 speed, 4X4, Smarty S67