there is a light line going down my screen

That’s unusual. I’d try pressing the reset button on the back of the calculator for at least two seconds. If that doesn’t work, then your LCD is likely just defective and you’ll have to use your warranty to get a new calculator. You can contact TI’s customer support here: https://education.ti.com/en/customer-sup... I’d love to have you repair the screen, but, unfortunately, it’s infeasible to get replacement LCDs.

If the line does go away, run an LCD self test to see if it comes back when certain things are displayed on the screen. To start the self test, press [mode]>[alpha]>[ln] then press [enter] until you see the ‘diagnostics’ screen. Press [1] to start the LCD test then press [enter] to cycle through each screen. Press [clear] to quit. If the line comes back at any point, then the LCD is definitely defective.