Cannot Place/destroy Blocks

Are there any messages in the chat when attempting to build/destroy?
Check your console for errors/messages if any as well.
Another thing is to check if the problem still persists without plugins. A plugin list would help as well.

 

Most probably it's a missing permission, But as DtigerCSK said a Plugin list would really help us to identify your problem.

 

What permission plugin do you use? And do they have the permission to even build?

Example of pex permissions:
Make sure you add build: true

Code:

groups:
  Member:
    options:
      default: true
      build: true
      prefix: '&8[&6Member&8] &e'
    permissions:
    - essentials.help
    - essentials.tell

Ask me if you need a GroupManager file.