Several states do not have a state income tax. So these states will not show up in certain drop down lists. Leave boxes 15, 16, and 17 blank when you enter a W-2 for these states.
Alaska, Florida, Nevada, South Dakota, Tennessee, Texas, Washington and Wyoming
This is actually a glitch. TurboTax is aware of it and working on it.
In the mean time, most people can just leave boxes 15-17 blank at the W-2 screen, because TN does not have an income tax.