State change question

Probably setting a variable (for example, "NoMoreHelp") as either T/F. The slide starts with the value as false, but clicking the Help button toggles it to true. Then the state of the button goes to "disabled." I would also suggest you modify what the button in disabled state looks like so that learners know that it's disabled (like the "no smoking" or "no parking" symbol - circle with a slash through it, or a large "X" overlaid on the button text).

Then, for subsequent slides, put a variable check at the start of the slide to see whether the variable is either true or false. If false, leave the button in the normal (active) state. If true (which means that at some point before this slide, the learner clicked it) leave the button as disabled.