Well, as usually happens, I heard a sermon on this topic last year and forgot about it. If you want to listen to the sermon, it is available as an mp3 here.
Here is why you should believe the Bible:
It is a reliable collection of historical documents written by eyewitnesses during the lifetime of other eyewitnesses who report supernatual events that took place in fullfilment of specific prohpecies. They claim their writings are divine rather than human in origin.
Don't believe me? Look up 2 peter 1:16-21.