After installing Tiger when it came out and even after upgrading to 10.4.1, my Sawtooth PowerMac G4 with a 1 GHz Sonnet CPU upgrade card keeps freezing when it is doing processor intensive tasks (watching movies, ripping MP3's, video in iChat, etc.). I've repaired permissions and repaired the startup disk, did a memory check with Rember (all OK, some permissions needed repair, and some blocks of disk couldn't be repaired). I wondered if the CPU was overheating because of my processor upgrade card. I opened up the case and the fan still seems to be running, although a little dusty. I left it running with the case opened and an external desk fan aimed at the CPU and whenever it crashes the CPU feels insanely hot (can't touch the heatsink for more than a second). Other times when I feel it it is sometimes hot, sometimes cool. I can't run any of the temperature monitoring apps like ThermographX since there is not temp sensor on my CPU. Any ideas if this sounds like a processor overheating problem, bad memory problem, or software install problem? I've run without any external peripherals plugged in, and put a second fan inside aimed at the CPU heatsink, and it seems to be happening less now. Where is the fan intake since it is on the enclosed side of the box? It's been in the 90's+ here recently, so I'd be overheating too! No obvious problems in the console logs, but where do I look for kernel panics? Thanks for the help.