Recently my G5 ipod started exhibiting all of the problem mentioned in this forum. Showing a full charge then going dead, not communicating with the computer just whirring and clicking and so on. from reading the other posts here I have concluded the the problem begins because the battery is allowed to drain to an extreme low and this for some reason gives the iPod a brain cramp from which it has great difficulty recovering.
This is a very frustrating situation because even if you can get your iPod fully charged it doesn't seem to realize it has a charge and hence all the other problems. I am convinced that it is charging but the HD refuses to recognize that the battery is charged. I have found a solution that worked for me but you will need an external charger to get the process started. Any sort of charger will do so if you don't particularly want to buy an adapter any iPod accessory with a charging base, like an iPod clock radio or car charger will do if those are items you are more inclined to purchase.
All you need to do is get the iPod functioning well enough to be able to do a reset and then put it into disk mode. I did this while the iPod was attached to the charger. Instructions on how to do the reset and set it to disk mode are here
http://docs.info.apple.com/article.html?artnum=93651. I then dashed over to the computer and while the iPod screen was still lit I plugged it in to the computer by USB. You need just enough power so that your computer will recognize the iPod when you attach it and then the USB will take over powering the iPod.
When iTunes starts up and begins to sync the iPod select Restore. In my case when that process was completed the iPod returned to the old "low battery please wait" message ( because it had restarted ) and no longer showed up on the computer so I disconnected it from the USB. I then turned the iPod off and on again, the apple screen came up and then I did a reset. Up she came nice and clean and with a full charge. Then all that was left was to re-connect to the computer and sync with iTunes since the iPod at this point is just as it came out of the box with no files on it. I think the crucial point is to get the iPod reset to factory and disconnected from the computer before it begins to sync your files automatically. If you don't get the "low battery" message as I did perhaps you should eject the iPod as soon as the restore is complete and before syncing begins in order to emulate the steps as I did them. I don't know for sure if prematurely ejecting the iPod is harmful so consider that step thoroughly before you proceed with it. My guess is that if iTunes will let you do it then it is probably OK.
I chose to sync only my audio files and not my movies at this point to save time and I will test for a few days to see if the problem is truly solved and report back.
I have no technical basis on which to explain why this series of steps worked for me I just know that it did. When you don't know why your iPod suddenly went mental it's bad enough but when the so called "experts" can't tell you what to do ( or care for that matter ) it can feel pretty bleak so I hope this information is helpful to someone.