Check your default audio output on your PC. Sometimes it changes by itself (ain’t computers silly). Mine suddenly defaulted to headphones once. I changed it back to my speakers and the audio came back on.
Other than that, sometimes PPro itself changes the default audio hardware. Go into preferences>audio hardware and if you have a choice of options (usually MME is the right one) play with those. By any chance, even without sound, are your sound meters moving when you play a clip?