A malfunction inside the iPhone can cause the screen to go completely white -- a situation commonly referred to as the "White Screen of Death," or WSoD. Although it can be disheartening to have a phone with a white screen, it doesn't really necessarily spell death for your phone. When caused by a software malfunction, for instance, the white screen is merely a way for the phone to protect itself.
Physical damage to the iPhone such as occurs when it is dropped, banged forcefully or exposed to liquid, is one reason why your device has a white screen. When the white screen of death presents itself after such physical trauma, it's likely caused by a disconnected wire on the inside of the phone. Specifically, it is caused by the wire that connects the internal components of the phone to the LCD screen. This wire is labeled with a "#1" sticker and can be reconnected by an experienced Apple technician. Attempting to reconnect the wire yourself isn't recommended, as it will void your manufacturer's warranty and potentially cause irreparable damage.
A software malfunction is another reason why your iPhone has a white screen. Software problems may occur from installed applications, iPhone driver updates or even iTunes application updates. In cases where a software malfunction is the cause of your phone's white screen, you will often notice a black apple in the middle of the white screen. Before you take it to the store for repair, try fixing the problem yourself by rebooting your phone. You can reboot the iPhone by holding down the "Sleep/Wake" button and the "Home" button simultaneously until the screen turns black and a white apple appears. If successful, your phone will load normally.
Another cause of a white screen on your iPhone is a failed jailbreak. If the white screen appeared after you tried jailbreaking your phone, try restoring the device back to its factory settings. This process will erase all the data from your phone, but may reverse the malfunction caused by the failed jailbreak.
When attempting to repair the white screen on your iPhone by restoring it to its factory settings, it's important that you don't select the option in iTunes to restore from a recent backup. In cases where the white screen was caused by a software problem, this problem may be present in the backup as well, making your phone susceptible to another white screen problem. Additionally, after the phone is successfully restored, download applications one at a time so each one installs correctly without an error. This is a good way to catch glitches and prevent future software problems.