Bart: "I have done that in my past with sincerity and there was no revelation of the existence of God. So where do you search for God?"
It begins in His Word. (John 14:21)
Now, I don't know you at all. So this is me sharing what I have observed and helped this hypothesis of mine.
There is something I noticed with many atheists, proclaiming Christians and false converts. They have one thing in common and this might have been you. It was me for many years, dare I even say 15 years, I thought I was a Christian. I received the word as many false converts with pure gladness. I was so happy to be(come) a Christian I went to church and volunteered and was very involved. The entire time I was false, sinned occasionally but that was OK, God was so forgiving. He wouldn't care, for example, that I went out Fridays to the clubs with the intention to fornicate. He loves me and I love Him. Happy, happy, joy, joy!
Flash ahead to a real dark place I was in. It was then I realized that I actually was a false convert all those years, that I was playing a Christian. Once I realized that fact, I was frozen. I was shaken to my core and I was actually afraid of God, the real kind of fear. (Proverbs 1:7; Proverbs 9:10)
I was a mess, broken, spent, and truly lost all over again. God allowed me to realize what a wretch I truly am. I approached God again but this time a very fragile, crushed, and a broken man. (Psalm 34:18;Psalm 51:17)
Words will never do the experience justice. An indication that I look for now a days isn't the happy story of becoming a Christian, its the dark and broken heart that I look for.
The other day I read something I could relate to:
"God never clothes men until He has first stripped them, nor does He quicken them by the gospel till first they are slain by the Law. When you meet with persons in whom there is no trace of conviction of sin, you may be quite sure that they have not been wrought upon by the Holy Spirit; for 'when He is come, He will reprove the world of sin, and of righteousness, and of judgment.'" (Charles Spurgeon)
Science would have a hard time measuring the evidence that I now have in referenced to God. I am here to tell you that these days I know God exists and he has saved me once and for all and my name is actually written in the book of life and I am in awe daily because of it.
Thoughts are immaterial, emotions are immaterial, the mind is immaterial, none of them can be seen or observed, the lover experiencing the feelings of love to his loved one, they cannot be proven by science, only the lover can know that feeling that they are experiencing.
They are all immaterial just like the laws of logic, yet we do not question their existence just because we do not see them.
Once you experience God (and his love) it will be impossible to go backwards. You are changed, you are born again. Any truly saved Christian will tell you this. Just a mere 2-3 years ago I was saved and I experienced God.
If you want a good example of how a man responds to being soundly saved listen to Paul Washer's testimony