If a dead virus enters your body can it still harm you or make you sick?

Not if dead: That is the basis for some vaccinations.

No, it can't.: The only way a virus can make you sick is if it gets into your cells, affects the activity inside those cells, and then multiplies and spreads to other cells. And only a live virus can do that. A "dead" virus, like that found in the flu vaccine, absolutely can not cause the flu. On the other hand, any vaccine can possibly cause an allergic reaction, so i suppose it could harm you that way.