The president took the stage. Everybody stopped speaking. The ticking clock was all that could be heard, (compound-complex sentence)

The president took the stage. Everybody stopped speaking. The ticking clock was all that could be heard, (compound-complex sentence)

When the president took the stage, everybody stopped speaking, and the ticking clock was all that could be heard. // Everybody stopped speaking, and the ticking clock was all that could be heard when the president took the stage.