How to fix MineCraft crashing during launch?

My Minecraft has been broken for the past 2 months.
When you click "Play" is starts to load up as per usual. When it gets to the mojang screen, it says that it has stopped responding then eventually crashes.
I've tried everything - uninstalling and reinstalling, downloading files from a working MineCraft and uploading them, checking my drivers to see if they were outdated. Everything is updated, including my graphics, but it's still not working.
Any ideas on how to fix this?