My PowerBook makes a clicking sound but it won't turn on, why?

Memory modules are solid-state, they just don't click. Don't ever spray any type of lube into your system! While wetting a Q-Tip with some electrical contact cleaner to wipe down the memory module contacts could help. Spraying is a big No No! The areas you get wet will collect dust and other junk like a magnet!

Review Mayer's answer above - 99% of the time the HD has gone bad. You can prove this to your self if you have the original recovery CD that came with your system or a logo'ed OS CD you should be able to boot up with it. If you don't you'll need to get one or an OS install CD to re-install the OS in any case.

I will see if I can dig up the recovery disk and try to boot from it but like I said, I pulled the hard drive and hooked it up externally via usb to another mac and was able to copy stuff off of it. The clicking is coming from the optical drive as it is initializing on bootup. I am also going to try pulling the memory one piece at a time to see if that could be it. I will report back after my next steps.

It was late when I replied so I missed that tidbit, sorry ;-} That your drive is accessible externally from a second Mac, thats good! You still need to find the recovery CD to make sure the drive is accessible internally. Check your systems date & time (make sure your not connected to the internet when you do this) is it correct if not bingo! your CMOS batt is dead so your loosing your settings (boot drive setting) Which can explain why your optical drive is trying to load the OS instead of your HD's OS. Otherwise you'll need to re-install the OS as it's corrupt and don't forget to use the Preference Startup Disk to select the HD to boot from. If you can't see the HD then the drive cable is bad or did you replace the HD (this being the replacement drive)? If so make sure It is an Ultra ATA/100 drive and also double check your jumper settings Primary/Secondary (Master/Slave). Make sure you have it set for Primary.

No this is not a replacement drive. I am troubleshooting why the machine just one day decided not to boot up anymore. I am still trying to get ahold of the recovery cd, but in the meantime will any bootable disc work? I ask because I put a Windows bootable disc in and this is what happens - I hear the optical drive initialize and start to spin the cd, then it stops, initalizes again, starts to spin and stops, repeat, repeat, etc. Basically doing what it was with no disc in the drive. Do you still have faith the correct bootable cd will make a difference?

New problem: how do I eject the disc? Doh! There is a lesson in here somewhere: never give a PC guy a broken MAC to troubleshoot. Your help is greatly appreciated.

Hey you at least tried! Unlike those 'Other' systems you need a Mac OS disk as that 'Other OS Disk' won't startup your Mac ;-} Sorry you'll need to find it. To eject the CD/DVD restart the system and press & hold the eject key in the top right corner, or function key F12, or hold the trackpad button down.