Are you allow to do the attack part of HSS when entering hindering(with a non-flier)?

Hypersonic Speed
Give this character a power action and move it up to its speed value. It automatically breaks away and can move through squares adjacent to opposing characters. During its move, this character may as a free action make one close combat or ranged combat attack with its range value halved for the attack. This character must be in a square where it could legally end its move in order to make the attack.

Nope, a non-flier that enters hindering must stop his movement. HSS attacks are made DURING movement, so since movement has ended, no attack can be made.

This is different from Charge and Running Shot, which both allow combat actions AFTER movement.