need help, powerbook g4

[kiel367]

newbie here with a strange issue, when i start my powerbook up, i get the normal apple logo and spinning icon, then it flicks off then to a white line about a quarter of an inch across the screen, now, when i plug a dvi monitor in, my screen goes back to full screen, but hangs over ont he bottom so i have to have the dock on the left hand side, once i remove the dvi cable it goes back to the white line, i have reset it back to factory settings and the problem is still there, anyone had this happen or know of any solutions? thanks in advance, kiel.