What do atheists believe happens to you when you die?

It depends on the atheist.

This atheist believes that when you die, the "you" part of you ceases to exist. It doesn't go anywhere, doesn't experience anything, you just fade out and then stop existing. And then you will never exist again, just as you never existed before you were born (or conceived, if you prefer).

Your body continues to exist, and will gradually decay and be broken down and return to nature, one way or another.

I'm happy to believe that something else happens... if somebody can provide me with compelling evidence that can't be explained in any other way. So far that hasn't happened.