Program won't let me enter a number for medical expenses, but gets me to the page to enter it. How do I get past this?

I have come to the medical deductions section of the TurboTax.  I am on the page to enter our prescription expenses.   It tells me what I entered last year and has $0 for this year.   The "$0" is highlighted and I can click on it, but I can't enter any numbers.   How can I fix this?