I have an iPhone which I've owned for a year and a bit now, used. Yesterday the screen was having trouble responding to me, I'd click the home button to wake it but there'd be a huge delay, as if it couldn't tell I was there. Once I got into the phone, it'd be fine though. Then later on, it'd just be white screen after I'd locked it. I have to reboot to get away from the white screen, and it works fine, until locked I've restored the phone but still have the same problems. Can anyone shed any light onto what is happening, and why?