Non-working apple iphone black 16gb 3GS +

Hi, i have a black apple iphone 3gs 16gb non-working for sale. Recently had new screens fitted, both the digitizer and the LCD screen. After the screens were replaced it mysteriously stopped working. the only known problem is that it will not turned on. phone was working perfectly fine before the screen replacements. looking for around 45-50 pounds. Text or call me if you are interested or would like more info. Thanks