Hi,
if the picture is dark as well as the LCD screen most likely the problem is that the ccd sensor is faulty.
Here is a link to the Ifixit guide which will give you access to the sensor.
[guide|40463]
Here is a link to just one supplier of the Lens Unit assembly including the ccd sensor. There are others which may suit you better. It is only shown to give you an idea of the cost.
http://www.ebay.com/itm/Canon-PowerShot-SX260-HS-LENS-ZOOM-UNIT-ASSEMBLY-CCD-A0543-/331906012701