I got from a friend a powerbook 540c. He didn't know if it works because he hadn't power adapter and batteries. I bought a power adapter and two intelligent batteries which i connected them to the powerbook. I turned it on and it worked. It has Mac Os 8.1 installed and 36 mb ram. I left it turned on for a while because i had something to do. When i came back i saw that the screen became white. I can hear the hard disk working so i pressed the power button and i restarted the powerbook but nothing changed. Just white screen. What can i do?