How can you convince an atheist that Islam is the true religion and that Allah exists using proofs from the Quran?
An atheist does not believe in Quran so how would you convince him from Quran. First you have you make him believe that this world is run by a very complex and very orderly program which is beyond capacities of a human or human like thing. And there is one who regulates this program, there is one who has written the script of this program and this authority who has written code of this program has the ability to manipulate any part of this code at any time at will and we call this authority as Allah or God. Only when one believes on this reality then you can come to Quran or Prophet etc. There are more plausible reasons to this, for that one should strive and reflect.