That's a tough argument.
We all exist because we present new information that had not already been known in the universe. New information including, but not limited to, our position in space and time.
Unfortunately, thanks to our limited capacity, most of the universe does not exist to us because we only have our five senses to retrieve information. To us, our imaginations are just as real as anything else.
However, with our collection of consciousnesses we are capable of accepting much as existing without actually retrieving perfect sensory information from them.
Nonetheless, if the information is there, it exists.
Now, trying to prove to *you*, specifically, that I exist is impossible. You have to accept that the information is valid and I have no way of knowing if what is coming through your senses is even correct.