A simple and clear logical proof that Islam is not from God is this. God who is claimed to have dictated the Quran is supposed to be omniscient- all-knowing and omnipotent i.e. all powerful. For such a God, it should be very easy to do something which is beyond the reach of ordinary humans like Muhammad, in the Quran itself, like to be able to predict in 620 AD that man will go the moon in 1969 AD, or for that matter, to give the then-unknown chemical formula of water, or to write a then-unknown language including modern Arabic, or Bangla. But nothing of this sort is done in the Quran. Of course, as we have seen, Muslims forcibly try to find 'miracles in the Quran, which are nothing but Islamic hoaxes and none of them is in clear language. The closest that the Quran comes to doing something like this is predicting victory of Romans, but that too is no miracle because both defeat of Romans at the hands of idolator Persians in AD 614-15 and the subsequent victory of Romans over them in AD 628 happened during Muhammad's own life -time, and the Quran, as claimed by Muslims themselves, was finalized during Caliph Uthman's period who ruled till AD 656. Also, scholars have shown that the Quran was edited and altered till AD 933, when it was finalized at last. And the Quran contains many contradictions, and many other mistakes as well.
Now, it is the view of many people, including both Muslims and non-Muslims that the Quran cannot be translated. This is what is written by Mohammed Marmaduke Pickthall in his translation of the Quran (Madhur Sandesh Sangam, New Delhi, India, 1995 AD). He says that the Quran in English or any other language can never take place of the Quran in Arabic, nor is it meant so. This shows that the Quran is meant for Arabs only, since Arabic was not, and has never been a world language. If God sent mankind a book, He would have given it in a way whereby it would be equally effective and charming in all the languages of the world. Or, as a minimum, he would have made the whole world know Arabic very well, so that it could understand the Quran very easily. A God who keeps his Revelation in a language which only a mortal human being knows cannot be termed as an All-Powerful or wise God.
Why didn't God do anything which could not have been done by humans like Muhammad? As a minimum, he could have revealed the Quran in a language which was known at that time, but not known to Muhammad, such as Sanskrit, Tamil etc. Muhammad dictating a Quran and getting it recorded in a language which was not known to him could have been some proof of God's help. If Muhammad came to guide humanity, and got the Quran revealed as a Divine book, why didn't God reveal the Quran in all the then-known languages of the world? The very fact that the Quran is very difficult to understand, it cannot be fully understood without the help of Hadith and Sira, the Hadith's are unreliable many of them are outright forgeries and they came into existence 120 years after Muhammad's death shows that it is not from God. A true God would have made his book understandable to all, easily arranged in chronological order, with proper details of which verse was revealed when, instead of allowing humans to get it written on trees, bones of camels, stones and then putting it together arranging the chapters in any order, starting with the longest first and the shortest last, with no clear certainty of which chapter was revealed when and all this compilation of the Quran done a good 20 years after the death of the man who dictated it, and claimed to have received it from God. A true God would also have given details of the life of his Messenger in the Quran itself, or written another book on it with no forgeries. As a minimum, he would have done something which is beyond the reach of Muhammad.