The program will not allow me to enter the Tuition fees for my college aged son. It has $0 grayed out.

To enter your 1098-T information:

1.  Go to the Federal section of the program
2.  Select "Deductions & Credits"
3.  Select "Expenses and Scholarships (Form 1098-T)" and click start

Make sure you select "Edit" next to your child's name so you can enter your 1098-T information.

Continue through the screens and answer the questions as applicable. TurboTax will determine which credit you qualify for based upon your answers. 

I follow the directions and it keeps saying that I entered it earlier.

Go through the entire education interview until you reach a screen titled "Your Education Expenses Summary".  Click edit next to the student's name. That should take you to a screen “Here’s your Education Summary”. Click edit next to the section you want to change; tuition, in your case.