Presence or absence. That is all. The DNA is the same regardless of whether the entity is alive or dead. But something is definitely "absent" in the latter case. We know this intuitively, we know this from direct observation. But that "something" may prove extraordinarily difficult to "isolate" experimentally.
It's something worth thinking about because that "something" seems obvious for straightforward examples like rocks and humans. But it is much less obvious for entities like viruses or viroids or even prions. Along those very murky lines, it is not obvious to anyone what constitutes life and what doesn't. Scientists draw up very precise definitions to include or exclude certain entities from life. And not all of them agree. There is no sharp dividing line and where a dividing line is drawn, it is done with definite measurable criteria. It's clear from your answers that even though you claim a sharp dividing line, you don't really know what that line is. You're in good company!
In thinking about abiogenesis, the same murky life-non life distinction exists. Afterall, nobody is suggesting that humans sprang from rocks (accepting some creationists). The gulf between life and non life is certainly not as clear-cut as you proclaim and it is possibly not a very big one.
Chiming in on a very difficult subject, I tend to agree with Nebullis. You state that the dividing line is "presence or absence," but that begs the question -- presence or absence of what? And if it is presence or absence of animation, this seems to apply only to the most rudimentary of examples -- biological life forms that have lost a preexisting animation.
The more difficult questions apply to the border line chemical structures, such as the (now proverbial) virus, which exhibits both dormant and active states. For that matter (to get really obtuse), we can measure both growth and cessation of growth in crystallization, and the chemical triggers in that process definitely have on and off switches. While these are certainly in a different category from biological life, they do render animation itself as less than a unique trait, or marker, of "life".
Perhaps the only (facetiously) known quality of life is its apparent weightlessness.