First of all, you should know that God isn't interested in us simply believing that he exists, but that we give our life to him and worship him.
"You believe that God is one; you do well. Even the demons believe—and shudder!"
(James 2:19)
Second, it's not necessarily true that people will bow the knee to God if he showed himself in the sky. I would bet many would think it's obnoxious, and others would call it magic, or find some other explanation for it as we do all the time. Remember the story of the Israelites and Moses? Even after God delivered them from Egypt and did many miracles for them, as soon as Moses left up mount Sinai to get the ten commandments, they made themselves a golden calf and worshiped that!
God has made it evident that he exists, you can see it all around you, in you, and through science and common sense if you think about it (where did the universe come from, etc...). There's plenty of evidence if you look! Most importantly though, God can be experienced directly by you, if you seek him he will make himself known to you. God is not some abstract entity that we believe in, but rather our heavenly Father who wants to have a relationship with us. Religion won't help you here, you must repent and surrender to him, seek his kingdom and pray for his presence in your life, go to church and let born again Christians pray for you.
"For what can be known about God is plain to them, because God has shown it to them. For his invisible attributes, namely, his eternal power and divine nature, have been clearly perceived, ever since the creation of the world, in the things that have been made. So they are without excuse."
(Romans 1:19-20)
Lastly, God does miracles and heals people all the time. You can find plenty of videos like this on Youtube, hundreds of thousands of testimonies from people all over the world. Watch this video for one example:
youtube.com/watch?v=8NfNSAQJvN0