My mac G4 powerbook doesnt start up. There are

You need an Apple modem.

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replace the battery

Are the contacts for the battery on the laptop good, no corrosion or anything?

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If there's no chime, your problem could be anything from a dead battery or bad AC adapter to a dead logic board.
Does the tip of the adapter on your AC connector light up? If not, that's a problem.
When you push the button on the battery, do you get at least two glowing LCDs? If not, that's a problem.
Otherwise, try the following: remove the battery and the AC jack to make sure the machine is off. Now insert the AC jack, and reset the power management unit by pressing the following multi-key combination:
Shift Control Option Power-button
Wait five seconds, then press the power button to attempt to start the computer normally.
The instructions above are for the 1.5GHz PowerBook G4; the instructions MAY be different if that is not your model.

Your PB can't find the system. Most likely you hard drive is no longer working. To check that this is the case, start up from the discs that came with your computer.You will need to replace the hard drive then re-install the operating system off those discs. I hope you had a backup of your data!

MAY be you need to change a laptop battery.
http://www.it-battery.com/apple-laptop-batteries-c-77.html

you can get low price and high quality battery.

Hello, You can test your adapter using a voltmeter and see if the power comes in Best regards. The best is actually to test with another adapter

Do you have any external harddrive attached to it? If so, remove it before restarting. Try to start it up in safe mode by holding the Shift button down at startup: http://support.apple.com/kb/HT1455

pull the battery out, put it back in, plug the mac in, and hold down the power key till u hear the chimb

If the magsafe is plugged in to the laptop and the wall outlet you should see a amber light on the plug. Once your laptop is charged the light will turn green.