Minecraft Problem? (20 characters)?

Some sort of glitch seems to have come upon my minecraft recently. It started when I switched between Adventure mode to Creative mode and back. When I switched back to adventure mode, trying to pick blocks with anything other then it's designated tool (e.g. shovel for dirt, pickax for stone, etc.) would result in nothing happening. For example, trying to break dirt by using another dirt block wouldn't do anything to the block. This only occurs in the world in which I was playing when I switched modes. Not sure what I did or how to fix it. Any help would be much appreciated (I know next to nothing when it comes to computers or minecraft so it might take some detailed explanation and I'm sorry for that).