When this kind of problems occurs ur CP''s Flex Cable*
is the faulty part in this case.
Solution is : replace the Flex Cable of ur 5200 (its a piece of cake)
1/ purchase the part click here
2/ take the phone apart using the screwdriver Number 6 for nokia Cp's.
3/locate the flex cable connectors on both mother boards LCD and Keypad.
4/replace the old one with the fresh one .
PS: a flex cable of Nokia 5200/5300 lives about 100 000 slides
so slide the phone just when u gonna need it!!!
5/close the phone after making sure all connectios are ok..
7/ plz do ratet this post as good as u can!