Can a player bring there hands over the net to hit or block a ball?

Depends..........player may never attack a ball completely on opponent's side of the net, but can in some circumstances legally block one - see below for details:

Ref NFHS 9.6.3: A player shall not contact a ball which is completely on opponents side of the net unless the contact is a legal block.

and 9.6.4: Blocking a ball which is entirely on the opponent's side of the net is permitted when the opposing team has had an opportunity to complete its attack. The attack is considered complete when:
a. Attacking team has completed its 3 allowable hits
b. Attacking team has the opportunity to complete the attack or in official's judgement has directed the ball toward the opponent's court.
c. Ball is falling near the net and in official's judgement no member of the attacking team could make a play on the ball.

cdhfsh, block the ball - yes, as long as the attack is considered to be complete by the opponent. Attack the ball (i.e., hit the ball) - not completely over the opponent's court; the ball has to be within the plane of the net for an attack hit to be considered legal. The Toolman stirred you right on this issue.