I have a PB 3400c with the same issue. The screen generally will not light up but when it does, the screen is all messed, then the unit crashes. The cable and everything in the unit is perfect. I suspect it is bad VRAM and it seems to be a common issue with this particular model.

I am thinking of trying to mash together a 190/5300 board with the case, screen and CDROM of the 3400...maybe it will work. Need a crap 5300 case with a good board to attempt this though.