Nothing really exists.
There's the past. The past is what used to exist but no longer does. We get to it basically through our memories.
The future is what will exist but does not yet exist. No matter how much we want it to – we will never experience the future.
The present is a tricky little thing. The problem with the present is that everything we perceive (that is everything that we receive through our senses takes time to be processed (even if only in a few milliseconds). So essentially everything we experience as now is essentially in the past which we already know no longer exists.
So is it possible to prove that you exist right now…
Well, something to chew on – especially at those times when start feeling particularly self important.