I have found a cure for this. I went into Setup and then into Advanced and Disabled 'Turbo Mode' which is described as follows:
Enabled/Disabled Turbo Mode to allow processor to assess its own thermals, current & power to come up with a dynamic upper limit on its frequency benefit -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1536721 Title: System freezes To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/compiz/+bug/1536721/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs