I have (1) 12/3 wire coming in to the box for the dimmer switch, lights started blinking, 3 lights on this circuit and then they finally went out. When I checked the wires red, black and white, white to ground read 120 volts, red and black to ground read nothing, white is the only one that's hot what would cause this could squirrels in the ceiling bit through the black or red and caused white wire to read hot now? Ty for any information
You have a switch loop
"One cable into the box" is the dead giveaway.
And an old-style one, from the sound of it. This is using white for always-hot, as Code requires. The other two are switched-hot, to allow separate control of two things, e.g. two banks of lights, or light+fan.
It's possible the last installation fed both switched-hot wires from the same dimmer, or the fan is missing. In such a case, it may be possible to rewire the switch loop to use white as actual neutral, black as always-hot and red as switched-hot, in the post-2011 wiring style.