I disconnected the power cord on a G4 MDD dual 1.25 to reset the firewire ports and now the unit will not power on. When I push the power button it flashes on for a sec and then nothing happens. I tried doing a SMU reset and a different power cord to no avail. I have had this unit for about 6-7 years. It has 4 200 GB HDs installed and 2 GB of ram (I think). The battery is close to being dead because the clock loses time and date often when starting up (this can't be the problem can it... I thought the battery was just for time, date, and perhaps some ROM info). I think the power supply died. I am not sure if it is worth ~$200 for a new power supply, yet I need this desktop for the HD and PCI card capacity. I cannot afford a new Mac at this point. Any suggestions and help will be greatly appreciated. Thanks in advance.

In some of the MACs I worked on the battery was necessary to turn it on, so it may be true on this one. Try DigiKey Corp. | Electronic Components Distributor | United States Home Page first for a battery. I remember going through a bunch of Macs just to replace the batteries.

I have a G4 Quicksilver with a similar problem. I will sometimes push the power button and it will flash but not start up; other times, it will start up but then shut off after 5-20 minutes. I have been trying to find out if the "relay" (I'm sure it is electronic now) is in the power supply or the motherboard, but since I got a used power supply for about $40 on eBay, I went that route to try and solve the problem. It has not arrived yet, but I will let you know if it solved the problem.
By the way, if you type the model number of the power supply (nothing else) into the eBay search engine, you will find your power supply easily (for my computer, it was ARI1PC12). Several choices were listed, but try to find free shipping and a warranty.

Hi -- having a good CMOS battery in you computer is always good. You can get them for about $5 at Otherworld Computing (macsales.com).

You can get your MDD power supply repaired for about $60 with a one year warranty at http://natramelec.com/ National Ram Electronics.

http://www.smpstroubleshooting.com/2011/12/smps-troubleshooting.html