DELL INSPIRATION SCREEN LCD PROBLEM

I HAVE A DELL INSPIRATION 8000 THAT THE LCD WHEN IT POWERS UP LIGHTS COMPLETELY UP BUT BY THE TIME IT IS FINISHED BOOTING UP IT GOES DOWN TO A 6 BY 6 INCH SQUARE WITH A FULL DESK TOP PICTURE IN IT JUST REDUCED IN SIZE. I’VE BEEN TOLD I NEED TO REPLACE TH LCD AND OTHERS SAY ITS IN MY SETTINGS. I DON’T KNOW WHAT TO DO ANY ADVISE WOULD BE APPRECIATED THANKS.