Computer Is On But Screen Is Blank (black)


First off I'm a fairly advanced Mac user for someone so new to the mac world but there's still much for me to learn otherwise I wouldn't have come here. My problem is as follows; I bought a used Powerbook G4 Titanium 800 Mhz (DVI) about a month ago and when I got it it worked fine. Soon enough though after using for and hour and over, it started overheating (this isn't my problem) which was easy to get around by the usual mehods; proping it up, coolpad, etc. Then soon enough after using that much more the screen would randomly go berzerk by skewing all the lines as if all the pixels suddenly shifted in different directions; and so I simply opted to not use it for such extended periods of time all at once. But finally today I was doing some downloading which took up quite a bit of time despite my broadband connection, and after hours of downloading and web surfing; it was pretty overworked and overheated so I turned it off and let it sit. Two hours later I finally came back to use it again and realized that it actually was turning on; I could hear it start up; keyboard lights would light up when pressed; and so on, but the screen stayed black. I 've waited and waited, turned on and off several times but it stays the same; computer on, but the screen is black. Where do I go from here??

Welcome to the forum.

Did you get a packet of CDs with the powerbook? If so, check for Hardware Test CD and use that to check over the machine. This will help in determining if the problem is hardware related.
If it comes clean, use the OS X disk that matches what you are running and start up the powerbook with it. Make sure you have the power adaptor plugged in before you start.
Insert the CD, restart the computer, and immediately hold down the c key.
When the installer screen comes up, do not click on that.
nstead go to the Installer menu and select Disk utility.
When that opens click on the second icon in the side bar at the left, then click on Repair Disk at the bottom right.
Watch the activity screen. If it does any repairs - you will need to click on the Repair Disk button a second time after the first pass is done. The object is to make sure it finds all the problems and repairs them. You may need to hit that button a third or fourth time to get no references to repairs made.

Now click on Repair Permissions.

When that is done, quit Disk utility and restart the computer.
But he can't seen anything on screen.

What happens if you connect an external monitor?