Then you might try to slide both sliders hard right. Both sliders hard left turns out the backlight and sets contrast to minimum. Try to set the backlight to max. intensity and fiddle with the contrast slider. Some of these machines need to get readjusted after some minutes of use, or the screen contents become unreadable.
The PB 160 contains a 3 Volt Lithium cell, soldered onto the little board containing the speaker and backlight controls. This battery will be dead, most likely, causing some kind of amnesia when disconnecting the power adapter and the removable battery. After you managed to boot the system successfully, you might consider to fix this issue. The machine is very well engineered, but please make sure to take precautions to avoid damage through electrostatic discharge. The CMOS devices on the board do not like to be exposed to more than a very few volts. If you want to use a multimeter, make sure to use one with a maximum test voltage around just 1 Volt. Some multimeters use higher testing voltages, and might fry the motherboard just by checking a line. I verified this on a motherboard and a backlight control board as well, sadly.
But before attempting to dismantle the PowerBook (with a tutorial), get it up an running. Shut the computer down, put the disk labeled "Install me first" into the floppy disk drive and switch the computer on
