Hi everyone, I use a Power Mac G4 Cube, 1.8 GHz. It has a Sonnet CPU upgrade. I powered up the computer this afternoon and used the system profiler. There is this strange thing: It shows that the processor is a 0 MHz PowerPC G4. I restarted the machine, but nothing changed. I wanted to reformat the hard disk and install Mac OS X Leopard, but when the installer loaded and prompted me to use a language to continue, the next message is that this operating system cannot be installed on this computer. This was the time I checked system profiler and saw this "0 MHz PowerPC G4" message. Power On Self-Test: Last Run: 7/24/16 6:03 PM Result: Failed Failure type: External cache So, the external cache causes this. And every time it boots up, power on self test fails!!! Can I do anything about it? Just hoping ... :-[ Does any of you have any idea why this happens? I had a backup of my latest configuration with Leopard, and restored it from an image. But if I had no backup, I couldn't install Leopard!! So, this is a major problem. And I am afraid this could happen if I try to install an application. Tried resetting the PRAM and pressed CUDA switch, but nothing happened! I am waiting for any help on this ... Spyros.