What will happen if a person with say weight of 100 kilograms, starts to travel with,
a) equal to speed of light?
b) greater than speed of light?
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The energy required to accelerate a massive object from below the speed of light to the speed of light (or beyond it) would be infinite, so it's not thought to be possible at all. This can be derived from the fact that the momentum $p$ of an object with nonzero rest mass $m$ and velocity $v$ is given by $p = mv / \sqrt{1 - v^2/c^2}$, which approaches infinity as $v$ approaches the speed of light $c$, and the total energy of an object, including both the energy due to rest mass and the kinetic energy, is given by $E^2 = m^2 c^4 + p^2 c^2$.
However, it would not be inconsistent with relativity to have hypothetical particles labeled "tachyons" that always travel faster than light; in order to get physically meaningful predictions about them, though, we would have to assume their rest mass was an imaginary number, as discussed on this page. Also, if tachyons existed and relativity wasn't violated, it would either have to be impossible to use them to transmit information faster than light (which could be a natural consequence of analyzing them using quantum field theory, as discussed in the link above), or if they could be used to transmit information FTL, this would imply they could also be used to transmit information into one's own past, violating causality (see my answer here to a question about why tachyons would violate causality). Although tachyons wouldn't violate relativity, there is no evidence that they actually exist.
