Show enough of your schematic as to be helpful.
It could be due to external loads, or that the supplies are not connected properly, creating internal current paths and some other failure mode has been induced.
Have you changed the code? Could it be running faster? Could you be driving a pin which is being driven by some other part of your circuit? Could you have damaged the IC with large voltages for other parts of the circuit or equipment attached to it? Shorted the board on a bench or conductive surface?
