iPhone stuck on dim screen, not responding to anything.

So this morning I was using my iPhone and I was setting a new contact picture. I had done it before with other contacts but for some reason the loading time to set this picture was unusually long. After about 10 seconds the screen slowly started to go dim. Not turn off, just dim. You can clearly see in the dark that the screen is actually on, but it's just black. I have tried plugging it into my laptop, but iTunes isn't even recognising the device. I have tried turning it off and back on, with no luck. I have tried soft and hard resetting, no response. I have even turned the phone off silent and back on silent again to see if it would vibrate, but once again no response. The battery was on around 96%, it had been charging that night. It isn't jailbroken and this is the first time I have had this problem with the phone (I have had it for two months now). I am not the first owner of the phone, I bought it off a really genuine guy who assured me that the phone was in perfect condition, bar a smashed front screen which I had gotten repaired the minute I got the phone and had been in perfecting working order ever since, until now. So the warranty is spoiled, so a replacement is out of the question I'd imagine. I really don't want to wipe all of the phone's data but if I really really have to, I will. Any advice would be greatly appreciated.

Thanks.