For reaching the speed of light, you need an infinite amount of energy, so you CAN'T reach speed of light in theory.

AFAIK, if some object reaches speed of light, from the viewpoint of the object, the space between it and its destination becomes 0, and time is passing infinitely fast. So travelling in speed of time is like travelling in infinite speed. And if it was faster than light, it would travel back in time.

An other problem of travelling in speed of light is that the mass would become infinite. So the force of its gravitation would also become infinite and it would suck in the whole universe in 0 seconds.