I’m sorry to hear about the problem. There are a few failure modes that would cause it to totally cease operation.
Most obvious: No power. Check that the batteries (if using) are good, or that your plug-in 5 V power supply is good, and that the power jumper is installed and in the right location. Check that there are good solder joints at the power connector/battery wires, power jumper, and at the pins of the chip.
Also possible:
* Reset problem, if pin 1 of the chip or the reset button has an accidental connection
* Clock problem, if the clock crystal or its two capacitors are not soldered well, or are cracked.
