The video cable is routed around the left side hinge. With heavy use this will cause the cable to weaken. Many owners have reported display problems such as random lines or a jumbled screen. A few have replaced just the video cable to successfully resolve this problem.
Here's the part: http://www.ifixit.com/PowerBook-Parts/G4...
Ifixit is out of stock but adds this warning:
Works in all 15" Titanium PowerBooks regardless of color of existing cable. Responsible for transmitting data from the logic board to the display. Installation will damage your computer's display if performed improperly. Specialized equipment is required for installation.
I don't really agree with this. Sure it's not easy but if you're here, you're probably good at fixing things. Care should be taken. The specialized tools needed are: 4mm Nut Driver, T6 and T8 Torx screw drivers and most likely a spudger.
I just resolved this problem with mine today by replacing the display data cable. I had to follow the 17 pages of directions here, then a few more pages from this PDF: http://www.PowerBookmedic.com/xcart1/fil...
The worst part of this is that you have to disassemble the LCD housing (the lid) and it's glued together with epoxy. Mine didn't turn out TOO bad but it's definitely battle scarred now. It did work, by the way, but it took me over 7 hours to do the repair and I'm no newbie.