Hi, I have a G4 . It was the last model built. 1.25 Single processor, 2 gigs ram, Ati 64 megs and running at 167 bus, firmware 4.3.? I bought a Mac 1.0 ghtz dual processor ( for £8.00, too good to miss and with a 7 day warranty ), to give me a little extra speed. According to all I have read it should be just a matter of removing the old and inserting the new. Not so! After inserting the DP and before booting I unscrewed the heat sink and checked for contact between the heat sink face and the processor. Two white contacts showed. I booted the comp and got a kernel attack. Switched off and rechecked the processor all appeared well. Rebooted only this time ( and several subsequent attempts ) all I got was 20 seconds of nothing and then the fan went into overdrive.( I have never heard the fan go into overdrive, this comp runs very cool, idle 22 C and never more than 29 C at its hottest ). During the 20 seconds of nothing the screen shows a " no signal " so I am assuming the MB isn't getting power. There isn't time for the processor to heat up to bring the fan on so its got me stumped. I put the 1.25 back in and the comp boots up perfectly. I would appreciate any help . cheers, Eddie. PS. The power supply is an ATX 350amp which I hooked up a couple of years ago after the original Mac PSU stopped working. Therefore the White 25 amp isn't available. Possible cause?