Games : Why can't I destroy blocks or hit people in multiplayer and in single player on diamond dimensions?

I am on Diamond Dimensions and I can right click a door or chest to open it, but I can destroy any blocks. I have tried everything, including re-downloading Technic launcher, but I still can't destroy blocks. I was on my friends world so I went to my world and it still didn't work. I made sure my control was on button 1 for attack, I made sure I was on survival mode and not adventure mode, and even tried dying to see if it works. It didn't. I can't even hit someone!! When a monster came near me I couldn't even hit him, I had to run away!! What else can I do?