Unclickable buttons

I need help! I need to make a jeopardy-like game in Flash. I need to know how to make it so that when a user click on say the $100, $200, etc. marks, that when they return to the money amount menu, those amounts that they already selected will not be selectable regardless of the order in which they chose the amounts, and will look different. Basically, I need to know how to make the program remember that a certain button was already selected and make it unselectable and look different. Sorry if this is confusing.