iphone 5c doing strange things!!

[gazzafc11]

Hi. I bought a faulty iphone 5c which was turning itself off. I have tested it though and found its not turning off, but doing strange things. It seems to do lock itself or suddenly come up with the "slide to power off" sign without even touching it. So dont know if its a faulty on/off switch. sometimes the screen flickers. Also, when you do turn it off, it turns itself straight back on again. Ive changed the battery, but still the same. There is no water damage either. Hope someone can shed some light on this and come up with a solution. Thanks in advance. Gary.