you unfortunately were on at a moment when there were no admins online to give you permissions to build and break blocks, if you are online next time send a messege to a admin if he can give you untrusted permissions.
Admin : leroyonly
those items are only banned in the world untrusted who is a world made as an anti grieving deterrent so less restrictions the longer you play
Admin : leroyonly
reactors and the other esential redpower items are only banned in untrusted a world made for the newly joined people those items will become availeble after you become a trusted player
Admin: leroyonly