"New Installation" button not showing

I bought Minecraft a few months ago, and I wasn't able to play it because the button where you usually add new versions is just not there... Whenever I watch a video of some sort of someone in the Minecraft Launcher, they have that button there, but no matter what I do, it doesn't appear. I've tried everything, even ticking the version boxes like "Releases", "Snapshots" and "Modded". If anyone knows how to fix this, please tell me.