Whenever the screen gets bright my tv turns off

Hello
Your TV goes out as you increase its brightness I thinks. It won't go out till a certain limit of brightness and will go out after that. You just note the level of brightness when your TV shut downs. If it is from the start itself, it will be due to problem in the ABL [Automatic Btightness Limiter] section, which is at the printed circuit board and has complex circuits related with it, that you can't rectify yourself, as it needs some skill and ability to follow the schematic diagram of your TV, and some solering concepts, and you should have to go for an experienced technician.
If it shuts somwhere near when the brightness control comes to its middle or so, it is due to an advance in the screen voltage, that you can adjust it at home. For that you should open the back cover of your TV. All care and precautions must be taken when we works with an electrical equipment. After open the back cover you just locate where the screen adjustment control is. It may be sometimes in the Line Output Transformer, other wice known as [LOT], or its picture tube base card itself soldered into. If it is with 'LOT' it will be marked ans "Screen", and will be an adjustable potmeter. It can be adjusted with the help of a screw driver of even by bare hand; if you have dare and experience to do. If it is in the picture tube basc card, there will be a mark printed as 'screen'.
Keep the tv opened, switch on it. Wait for some time, say upto 20 seconds, after the screen on your tv is alive, advance its brightness control to the cut point. Just do it a little reverse and see whether the screen comes alive or not. If not, switch off the TV again. Reduce the screen voltage a liitle behind by turning its preset to a little, so that you can see the screen again. Then advance the brightness control and see whether the screen cuts off this time or not. if it cuts off this time also, the fault is in the above said ABL circuit. You should get it repaired by an experienced tecnician. never use the TV at this condition for more. It may effect the emission of the picture tube. ok.