Hello, I want to purchase a PowerBook 1.67 15" off my friend that's display randomly blinks out. However, it works with an external monitor. Also, it repairs itself sometimes. I have a lot of experience with Macs, but is this a hardware or software problem? If so, how could I make sure? I will run a AHT on it and TechTool, but I figure it's the inverter or the backlight, the same fate as my PowerBook 400. Thanks.