In my minecraft PC's survival mode it will not let me break blocks.

My Minecraft PC edition does not allow me to break blocks in survival moded old worlds. This is not the first time. The only exception is flowers and grass. all it does otherwise is move my hand to the side. This is not on a server. And it is online. I hope you can fix this bug as soon as possible so I can enjoy my survival world.P.S, I have tried restarting my Minecraft and computer, but neither have worked.