My ZTE Racer was fine up until last night when the top half of the touchscreen became unresponsive. I turned the phone off for the night and when I turned it on this morning there was some improvement. Now it's only a strip of screen across the top that's unresponsive instead of the whole top half! Any tips on how I could fix it? I'm within the 1 year guarantee so if I have to I'll have it sent away for repairs. Any help would be appreciated 