Need help with Dell Inspiron 4150 Repair

Archived from groups: comp.sys.laptops (More info?)

I am trying to repair a Dell Inspiron 4150. It is a 1.6 GHz Pentium 4 with
SXGA+ LCD display. It had a damaged LCD and bottom case I when I obtained
it.The LCD and case have been replaced but the system boots only when
attached to an external monitor. When the external monitor is removed it
powers up, the LCD flashes briefly and then it shuts down. I also tried
replacing the video daughter card to no avail. It's a nice laptop and I
think it is worth fixing. Any ideas?

Thanks in advance.