We’ve had a few people recently report that their G4 (PCI video) Macs have ‘died’ and will not power up. Knowing how extremely rare Mac hardware problems are we just don’t easily jump to thinking they are broken. If this happens to you try resetting the Mac’s Cuda chip. According to Apple, this chip is in charge of turning the Mac’s power on and off, managing resets from various commands, maintaining the PRAM, and managing the real-time clock.
To reset the chip, open the Mac’s case (with the power off, please) and press the Cuda Reset button, which is located to the right of the battery.
Note: After pressing this button, your Mac’s clock is likely to be set incorrectly and you may lose some of the Mac’s custom settings that are stored in PRAM.