I bought Minecraft but can't play it.....I NEED HELP!!!!!!!

I don't know what is happening I bought Minecraft from Minecraft.net and when I click the download it will open up Minecraft wizard then there will be a yellow warning saying there is already an account. Then I downloaded Minecraft launcher and it would say downloading java then it would stop 3 fourths the way through and a tab would come up saying "unable to update minecraft runtimely environment PLSSSS HELPPPP!!!!