Alright, I've had his problem before, but it's happening again.
My Minecraft won't start because this message pops up:
Exception in thread "main" java.lang.NoClassDefFoundError: net/minecraft/client/main/Main
Caused by: java.lang.ClassNotFoundException: net.minecraft.client.main.Main
at java.security.AccessController.doPrivileged(Native Method)
I've tried everything that I did last time to fix it. I deleted and reinstalled Minecraft and I updated my Java (I have Java 8 Update 40).
I don't know what else to do and I really want to play. :c