By DIM do you mean the brightness is low? If yes have you tried increasing the brightness using the brightness option? Also do you see the same dimness when you are in the bios or is it only in the OS.
Now first of all you will have to stop turning it on. remove the battery as well. If you can access the MB then clean it with isopropyl alcohol, but that one that is used for electronics. use a clean tooth brush. Remove the LCD connector and clean it as well. let is dry for few hours and then test.