What would happen if Earth suddenly stopped rotating and revolving at the same time?
Two very different processes! First, if the Earth suddenly stopped rotating then the angular momentum would result in everyone and everything on the Earth's surface being flung sideways at a rate proportional to the distance from the Earth's spin axis. That is, no change at the poles, to 1670 km/hour at the equator. There would also be oceanic tsunami's which would sweep over all but the world's highest mountains. Or would they? The amount of energy required to suddenly halt the Earth's angular momentum is so great that its' dissipation would melt the Earths crust, and vaporize the oceans, so maybe there wouldn't be any oceans to form a tsunami, in which case we would all be caught up in a global cyclone of super-heated steam.
As for Earth ceasing to revolve around the sun, with no centripetal force to balance gravitational attraction we would simply start upon an accelerating drift towards the sun. However, If we assume that our moon stops orbiting the Earth-moon center of gravity, at the same time as Earth (presumably by the same hypothetical process as envisioned by the questioner), then long before we burn up with increasing proximity to the sun, the moon and Earth would collide, also by gravitational attraction.