My Dell Inspiron 1440 doesn't display after powering on

Compliements.
I have this dell inspiron 1440 laptop. The problem I have with it is, when I power on, the screen brightens up but I get no display. I tried power+D as suggested by a post I found, but nothing happens. But when I attached an external monitor, and I power+fn key, I get the pre-boot system assessment build 4119 screen, which perform the color bar and other series of test. But upon completion, I still don't get the POST screen let alone having it but normal, I need your assistance urgently.