Mac g4 added more memory won't boot up

The parameter ram reset will reset that and other basics back to factory without losing any data. To do this, take a moment and find the command, option, p and r keys and figure out how you are going to hold them ALL down at together. The mac should be off, if not, shut it down (not restart-shutdown). Now, touch the power button and immediately hold down the cmd-option-p-r keys. Hold them for the screen to cycle black to gray THREE times (each taking about 15 seconds), then let go and let the mac complete the boot cycle. On the second cycle, you should have already heard the "chime" appear. That's it! Good Luck.

1) Try the NVRAM and PRAM resets: http://support.apple.com/kb/ht1379
2) Remove any aftermarket memory and try booting
3) Boot into single user mode/ verbose mode which may provide more details on the problem: http://support.apple.com/kb/HT1492?viewlocale=en_US&locale=en_US

Have a look at the article on this webpage it may give you the information that you need to repair it http://support.apple.com/kb/TA26059

The ram might not be the right one. The ram that you put on there must be apple.

WHen you hear the startup chime, hold the shift key down. Do not release the shift key until you see the login screen. Then login and examine your System Preferences for something you recently added that is incompatible with your system. If you can't find anything obvious, use the Console utility to examine the system logs and see what error messages occurred during your earlier unsuccessful boot attempts.

try booting with control command P and R all pressed at the same time, wait for second chime then release.

If a Mac is shut down while the volume is set to zero, the standard Apple startup chime will not sound, so it is impossible to say whether or not this symptom indicates a problem.
For a startup issue such as this, I would recommend zapping the PRAM and resetting Open Firmware.
To zap the PRAM, start with a powered-down machine, press the power button, then immediately hold down the four keys: command, option, P, R. After ten seconds or so, you should hear the optical drive reset, and then the startup chime (because the volume is reset to full by this procedure). Ten more seconds, another reset, another chime. After the second time you hear the chime, release the keys.
Shut the machine down again (if it doesn't start up successfully, hold the power button until the power goes off). Press the power button, then immediately hold down the four keys command, option, O, F. You will see some tech-speak on the screen, then it will wait for input. Enter the following three lines, pressing the "return" key at the end of each:
reset-nvram set-defaults reset-all
After the last line, your Mac will reboot itself. It should now boot much more reliably. If it doesn't, chances increase that you have a hardware problem. You may want to run the Apple Hardware Test from the DVDs that came with the PowerBook to check your memory and logic board. Failing this, you are in for a trip to the shop.

I suggest you plug it into AC power, then boot with Command-P-R held down until you hear the unit chime twice, then release it. Hopefully, it will boot after this.
If not, boot with Command-O-F held down; when you reach the command line, type
reset-nvram [return-key]
reset-all [return-key]
If it doesn't boot after that, you have deeper issues if the machine is actually turning itself on and off.

there is a hardware fault or full hdd ...

thi guys will help Micromen - London

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.