Where did God come from? He had to be something before he became a spirit for we all have a spirit.
God's eternal existence, past and future, is certainly something difficult for us to grasp. We all have a beginning and an end, and so does everything we can see. So it is very hard to picture anything or anyone, even God, as not having a beginning.
The Bible does indicate that this is true about God, though. In Exodus 3:14-15, God says to Moses, "Thus shalt thou say unto the children of Israel, I AM hath sent me unto you. and God said moreover unto Moses, Thus shalt thou say unto the children of Israel, The Lord God of your fathers, the God of Abraham, the God of Isaac, and the God of Jacob hath sent me unto you: this is my name for ever, and this is my memorial unto all generations." I am told that the word translated "I AM" also means "I was" and "I will be" all at the same time. In Psalm 90, verse 2, we read, "Before the mountains were brought forth, or ever thou hadst formed the earth and the world, even from everlasting to everlasting, thou art God." God exists from eternity before now until eternity after now. In fact, we could even say God invented time because He exists outside of time.
In the book of the Revelation we also find that God is eternal. Revelation 1:8 has God saying "I am Alpha and Omega, the beginning and the ending, saith the Lord, which is, and which was, and which is to come, the Almighty." And in Revelation 4:11 we find, "Thou art worthy, O Lord to receive glory and honour and power: for thou hast created all things, and for thy pleasure they are and were created." Now it is obvious that God couldn't create Himself, so creating "all things" includes everthing but God. If there was anything else before God, He could not have created it. Instead, there can be nothing before God because He has always existed.
You say "He had to be something before he became a spirit for we all have a spirit." Why? We have a spirit, but we are not a spirit. On the other hand, God doesn't have a spirit, "God is spirit." (John 4:24) Again, it is a hard distinction, sometimes, to make. God didn't have to be anything before He became spirit because He is and always has been a spiritual being.
We have a spirit. Our bodies are inhabited by a spirit which we call the soul. That spirit came from God. "The burden of the word of the Lord for Israel, saith the Lord, which stretcheth forth the heavens, and layeth the foundation of the earth, and formet the spirit of man within him." (Zech 12:1) God gave man that spirit, and God will take it back. "Then shall the dust return to the earth as it was: and the spirit shall return unto God who gave it." (Eccl 12:7) Because we have that spirit, which comes from God, though we have a beginning and an end, that doesn't mean God has to have had a beginning as well.