Game only launches if I haven't previously started it (unless I restart my PC)

I don't know how you would replicate this issue, as it just appeared after days of playing perfectly with no problems.

I now have to restart my PC each time I play Minecraft. If I try to play the game more than once before a system restart then it does nothing after I click "Play" on the launcher. It hangs in the background, with no window, and uses memory but no CPU or storage access.

If I kill the Java process then the launcher will tell me the game has crashed but the button to view the crash log does nothing.