Hi,
This could be everything ! e.g. :

Electronic circuit defects,
connectors with bad contacts,
Broken (flat)cables,

Sometimes it's important to know WHEN the error occurred for the first time :
After bad weather with lighting ?
Did your keyboard fall or was it hit by mechanical violence ?
Did another accident happen e.g. fluids (drinks) to you keyboard ?

The best thing is to visit your dealer and let him find out what is wrong.

Roel