Dear Mr. njjen,
This problem can be fixed easily. contact any TV servicing store nearby. This problem can be due to loose connection in the PCB or can be a picture tube problem or a problem with iconoscope. cost depends upon the part which is to be serviced
you can bring more brightness by removing cover on your tv and then you will see ther 2 button ther in back of your tv one is FoCUs and other is G2 rotate the G2 button till you see more brightness on your screen put the cover back and that is if you dont know to do that go to one authorised service
Usually answered in minutes!