Lets say that when you open your Minecraft Launcher you don't see anything and it is all gray. When you click on the launcher it says it is no longer responding and crashes.
Go to your Minecraft data folder.
Windows: Press Win (Windows Key) + R. When you see a box pop up, type in
%appdata% then press enter. You will then see a folder pop up. Find the folder called
Linux/Mac: Refer to this article.
Reset your .minecraft folder
Once you see your
.minecraft folder, right click it and select
Rename. Rename it to
minecraft_backup. Please note that this will reset your settings, texture packs and worlds. To bring back your worlds, move the
saves folder from the
minecraft_backup folder to the new