I can't click on anything. I can't click play. Sometimes it allows me to but after that I can't click on a world. If I get onto world then I can't place blocks. It isn't a mouse problem because I can left click on other games I have and on search browsers. Does anyone have an answer?
I did once, accidentally, change the buttons required to place a block in the settings. To fix this, go to settings, options, controls and make sure attack/destroy is on left click. If this does not fix it, it may be an error that is only fixable by reinstalling java and/or Minecraft.