What probably happened is that the cable for the Digitizer got loosened or disconnected. Use [guide|62702|this] guide to open the phone up and see if the cable is still seated properly (If you don’t have the required tools, especially the heat gun, I’d advise you to get them. They’re vital for people who repair their own phones). If it is, then it may be a component of the LCD/Digitizer that is broken, meaning that you’d have to get a replacement. You can get the part from [product|IF347-000|here] or search online to find a cheaper alternative.
Carpe Diem,
Minas