Why is minecraft letting me destroy blocks?

I just updated to 1.7.4 and when i started a new world in that update but now when i try to get blocks and just destroy it makes me do it multiplie times and i've reset it multipe times and can't get it to go away i'm on single player in survival

Do you mean "Why is Minecraft not Letting me destory blocks?" If they keep reappearing.

If you can't delete a block then it might be because your still in the Spawn radius with protect blocks in the area of the spawn point.

If they is a delay and the block is being deleted, It could be server lag such as a bad connection to the server or the Server is spamming alot of commands on the server window.

If you need anymore help visit the Minecraft forums.

If you say that the blocks are making you destroy them several times, then it may be lagging a lot. Check your settings, and for best results, turn your particles to "minimum", Cloulds: OFF, VSync: OFF, Smooth lighting: OFF, Render distance: 2 CHUNKS or TINY, if you ever go back to 1.6.4. Also, it could be as luke said, and it won't let you destroy blocks simply because you are too close to spawn. This is to prevent things like lava killing you repeatedly, and very, very deep holes.

HOPE THIS HELPS.