Closing lid doesn't go to sleep

Same here. If I close the lid and hold it shut for a few seconds, it may stay asleep - if I keep some pressure on the lid, such as a few CDs or an iPod. I talked to an Apple tech, who said it was basically just wear and tear on the latch (and cable leading to it) over the years - nothing much I can do about it apparently.

I found out that there is a cable in the Powerbook that leads from the latch to the logic board - it detects whether or not the screen is closed, and can loosen over time. This seems to be what happened to mine. You also said that it cycles when the lid is shut - same thing with mine a few months ago. Now it just won't sleep with the lid shut at al unless I put some weight (such as an iPod or two) on the lid..

I'm afraid that there's not much that can be done if the latch is to blame and the connection is bad - since AppleCare won't cover wear and tear... I hope you can get it working again!

The lid-closed-sleep sensor is actually magnetic. There is a magnet in the screen and a sensor under or in the trackpad. I can sleep my PB by drawing a good magnet over my trackpad regardless of the screen position or latches. You can drop a paperclip on the top of the screen and find the magnet above the Apple stem.

It's possible that the magnet or sensor has moved, or the circuitry for the sensor has gone bad. However, I don't have a fix.

The lid sensor on the PB G4 is a magnetic sensor located on the back of the LCD panel. It is attached with a small amount of glue and a piece of tape. I have seen cases where the magnet has detached and is loose behind the LCD, but the sensor under the keyboard could also be at fault, which you've already ruled out. Resetting it however is no easy task and requires completely ripping apart your PB. Recommend you have it professionally done.

Well here's one for you...my PowerBook G4 (15" 1.GHz 1GHz RAM) won't go to sleep with the Power Adapter plugged in. I close the lid and the "sleep" light comes on, but when it gets to the end of the first "flash" (about 10-15 seconds) it powers back up...the Optical Drive makes a whirring sound and the "sleep" light stops. After about a minute it tries again...sleep light comes on, after one flash the Optical Drive whirs again, and it starts up again. It will keep doing this until I eventually put a stop to it, by lifting the lid...then, most times it won't awake from sleep (even if I close the lid again to try and re-induce sleep mode), forcing me to power it up with the Power button.
If I unplug the Power Supply it goes to sleep without trouble, and also awakens without incident.
I have tried unplugging any peripherals...making sure the Energy Saver settings are set properly (ie not choosing NEVER SLEEP)....
Any other suggestions?
Thanks in advance.

It is not hard to reposition the magnet, though it takes patience and slow progress. You will need 3-4 Small flat head screw drivers (used for prying, plastic works great because it does not scratch) and T6 Tork Screw Driver (Radio shack has it). Tilt the screen all the way back ward, until it does not want to go back anymore, don't force it. Then Unscrew the two screws at the bottom of the screen. Then take your screw drivers and slowely starting at the top corner where there is place to start, slowly pry the cover of, using the screw drivers slowley work your way around, here is a link to a more detailed guide, you can skip several steps by tilting the screen
http://www.ifixit.com/Guide/Mac/PowerBook-G4-Al-15-Inch-1-5-1-67-BT-2-0-LR/Displ ay/64/15/

It could be something silly like a keyboard protector not laying flat when the lid is closed. Here is my experience with the problem you describe:

I recently purchased a new Marware keyboard/screen protector for my MacBook pro 15" (Marware Protection Pack for MacBook Pro $19.99).

Due to the stitching on the edges of the microfiber protector the computer will not stay asleep when the lid is closed . This is caused by the stitching around the corners that prevents the protector from laying flat. The protector appears to catch a key (or keys) and hence wakes up the computer. The computer will then continue to run and will get very hot when the lid is closed instead of staying asleep. my old marware protector was just a foam rectangle and it worked great, so it is unfortunate that I lost it.

Hope you can figure it out, that is so annoying!

Make sure fax receiving is not enabled in the Print & Fax pane of System Preferences. There are also some USB printers, scanners, and multifunction machines that aren't sleep-savvy and will constantly re-awaken a sleeping Mac. The only remedy for that is to disconnect them when they aren't in use.

I am having the same problem and no adequate solutions have been posted.

As stated the machine does not stay in sleep mode but cycles in and out of sleep when the lid is closed AND the power adapter is attached.

On battery power it sleeps as per normal with lid closed.

Any ideas?