My power book g4 will not start up it goes on with a white screen and the apple sign with the wheel spinning than it goes off

Unfortunately this could be a sign of the hard drive having failed. To test this I would like you to try a few steps for me.
1. Remove all devices and power off the computer. (Sometimes you have to hold the power button for 15 seconds)
2. Locate the following keys as you will need to hold them down will your computer starts; p, r, Command, and option.
3. Power on the computer.
4. Immediately press and hold the following keys; p, r, Command, and option.
5. The computer will cycle, after you hear the chime finish the 2nd time you can release the keys.
6. Test computer.
If that doesn't work...
1. Insert the system disk that you received with your Mac into the drive with the computer on.
2. Remove all devices and power off the computer. (Sometimes you have to hold the power button for 15 seconds)
3. Hold down the letter c press and release the power button.
4. When you see the Apple on the grey screen you can release the letter c.
5. Select your language.
6. At the top of the Screen select Utilities then Disk Utility.
7. In Disk Utility check the left side to side if you hard drive is listed.
8. If it is not listed you will need to replace your hard drive. If it is listed you have a separate problem.

I think your system files are corrupt try to reinstall mac OS X

probably the software is courrepted.boot the system with installation disk and then check the disk with diskutility.repair the disk permission and check.if still the issue persist.reformate the drive and install freshly

I had a problem with my hard discs. That's where I got, but my screen froze after a few minutes. try pressing apple + s after the chime. See if you can search around there. Also, try holding the shift key when you hear the chime, or when booting if you don't normally hear the chime, and hold it 'till you see the apple logo.

i have the same problemmm=[

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

If you have the original install CD or the OSX CD, boot to CD. To do that you must insert CD, restart PowerBook and hold letter "C" on keyboard while computer is starting, then take the first steps towards installing the OS, when you get to the bar on the top go to Tool>Utilities>Disk Utilities then select the drive a do a disk repair. That may fix the problem and bring your system back to booting normally.

I've read that aftermarket DVI cable adapters don't work well with this set-up. You might try the Apple DVI to ADC adapter. It's expensive but I see them on eBay or craigslist from time to time at less than half the normal $99 cost.

look closely at the screen. You might have to change the lighting or shine a powerful light from the back of the screen, through the Apple logo. If you see a dim image, your problem is either with a bad "inverter" board, a bad "CCFL" light (the bulb that lights the screen), or with the logicboard itself. check back for more info if this is happening.

Which screen is it stuck at? The spinning "gear"? The Blue progress bar scree? or the login screen? Answer this and i have your answer.