Google adds not showing on all my pages

I have 4 pages as tabs across the top of my website. All should have three Google add blocks on them. My problem here is the home page has one add, the second page has all three adds, the third page has two adds and the fourth page has the three adds.I cannot understand what is causing this.Any ideas would be a great help.when you click on each page they appear to load for a split second and then it just leaves a blank space instead.