I agree with the power supply being possibly bad. I don't know the voltage of the 520 series. it may be on the bottom of the laptop on the UL sticker. Another problem with these old Powerbooks is that the electronic components get old and fail. I have a Powerbook 3400 that worked great, then I tried to turn it on one day and it died mid boot sequence with an burnt electronics smell. I collect these things but I get more paranoid about turning them on as they get older.