Blocks won't break unless with right tools? [duplicate]

You are most likely playing in Adventure mode, which may have been a result of accidentally clicking one of the option when setting up LAN. To solve this, type /gamemode s or /gamemode "username" 0 If you find that you are unable to do this, do the following:

• Close the LAN Server
• Open the world you play on and then click open to LAN
• Enable cheats (for future use) and then set the gamemode to survival
• Let the games begin!

Without the correct tools anyway, it would have been hard to escape from the cave.

Despite what you say, the only explanation is that you are in fact in adventure mode, not survival. Issue the following command to change the server back to survival: /gamemode s. If you are not an operator, this will have to be done in the settings (which means restarting the server), or in the server console (omit the /).