The reason your iPhone screen stopped working (https://devicefixes.com/blog/iphone-screen-not-responding-to-touch/) could be because of physical damage, software malfunctions, or environmental conditions such as water and extreme temperatures. Although the screen may look okay, the internal parts may be broken once they drop or when used over a long period of time. Display can also be frozen by software bugs, thereby rendering the display absolutely unresponsive. It is necessary to figure out the cause of the malfunction to know whether a simple fix or repair is required.