I don't believe in a God I can't see
Most all of us browse the Internet daily. We read hundreds of pages of information written by people who we 'do not see', yet we believe in what we read. Why is it, people can't believe in the creator of Heaven and earth? I believe it is because of our inherent nature. We need proof that we can see or touch with our senses. Even when that 'proof' is provided, there are those that still have doubt. It has been like this since the beginning of time. The Jews didn't believe in Jesus, even after witnessing the miracles He performed. They accused Him of being possessed by a demon.
There are numerous reasons why people do not believe in a 'God they don't see', and after you speak to those people, you'll soon find out that their reasons go beyond not being able to see Him. Those reasons vary from why does God allow suffering (see the page http://godisareality.com/suffering.htm on this site. It can be found under the Questions and answer section) to why does God allow some bad people to prosper and some good people to stay poor etc.
It is because of our sinful nature that we are fully separated from God. Man is incapable of fully understanding God on his own. But Blessed are those that have the insight to see beyond what we can feel, see, smell or hear. Jesus addressed this issue of not believing with the disciples when He was speaking to Thomas, one of His disciples (this is where the term 'doubting Thomas' comes from);
“Jesus said to him, “Thomas, because you have seen Me, you have believed. Blessed are those who have not seen and yet have believed.” John 20:29