@Musik: If you dial *#0*# into your telephone keypad and select Red, Green and Blue from the options on screen, does the white line show up in any of these tests? If so then the issue is hardware related and will need to be looked at by one of our engineers at an authorised Support Centre. To find your nearest one please check the link below, select 'Mobile Device' and enter your post code.
@Musik: It's possible that the fall resulted in some physical damage to hardware, therefore please visit your nearest Support Centre via the link above and an engineer will be able to inspect and repair the device for you. Please be aware that if physical damage is deemed to be the cause of the issue then a charge will be applicable to cover the cost of the service.