As a new member I'm posting this info as an insight into some of the problems I went through on this computer and the final total solution. I hope it may be of use to others. Background: Shortly after purchase in Dec. 2002 Apple came up with a power supply replacement program in response to the noise problems on these "wind tunnels" So the power supply was replaced in early 2003. I use CorelDraw 11 Graphics Suite for photos and drafting and about 3 years ago it started to lose functionality in several area. Tried new clean installs of software and OSX but nothing worked. Then on an archive and install of Leopard the computer shut down instead of re-starting. This then became a regular occurrence, plus it would shut down instead of sleeping. Then external drives would not mount at all unless the power cord was pulled with the computer running. Next there were a series of problems with what looked like HD failures. Disk utility reported imminent HD failure on internal HDs ( 4) I tried every re-set, new batteries, removing PCI cards, booting with no external USB or anything else. Ran Disk Warrior and the Apple Hardware Test and all reported no Hardware problems. But slowly things got worse to the point where I had to try 5 or 6 times to get the computer to boot. Eventually I gave up and went to my 2 intel Macs but they don't like CorelPhoto-Paint. On a whim I finally decided to physically strip the G4 of everything, do a thorough clean and then install the original HD with original minimum Jaguar as OS. Safari wouldn't work. Firefox was just usable but the whole system was very unstable and all the bad symptoms were still there. Then the EUREKA moment! I put the original power supply back in (yes I'm a pack rat! ) but left the replacement fan installed. Booted into Jaguar and let it run. It went to sleep! It woke up! It re-started! Then the big one. I had put one HD with all my files and apps as well as Leopard in a bootable firewire enclosure. Plugged it in and used it as a boot drive and it worked flawlessly, not only that the original Corel installation was still on it and that was also in full working order. Plus it runs quieter than it has ever run and CPU temperature rarely goes above 48ºC So now I'm happy to report a fully functional G4 with all the old legacy software totally usable and full sleep and wake capability. Just like a Mac should work. Hope this helps someone else.