17" EMC 2114 (A1208) display not turning on with the power

hello people willing to help . iv just opened up my imac to find LED3 or 603 isnt working then i read that led3 indicates that the computer and the lcd display are communicamting when the light is on however my led3 is off so pretty much just wanna know is there a quick fix for this or a part i need to get and if so what do i need and where would be a good place or site to get it from . i dont really wanna take it into a shop if i can do it myself . thanks for reading