In case anyone experiences these symptoms...

I am running Ubuntu64 8.04 Hardy Heron and kernel version 2.6.24-19

Today, without any warning, my system froze. I had to hard reset and upon boot of Ubuntu the system went into sleep mode (power led flashing) shortly after the Ubuntu logo appeared.

I rebooted again and tried a safe boot into Ubuntu by pressing ESC before boot. Same issue - Ubuntu logo appears then system goes to sleep.

I started to get nervous so I grabbed my Ubuntu64 LiveCD and prepared to boot off that so I could backup my data. This time on the reboot the system didn't even finish POST when it went to sleep.

Hmmm. I got to thinking that I must have a power issue or heat problem regardless of the fact that I do not overclock my 3200+ processor. I cracked the case and fired up the machine and low-and-behold the power fan was not spinning! I quickly shot into the BIOS and check the health and the cpu temp was 181F!

I gave the system some time to cool off and then I moved the cpu fan leads to a different location on the mainboard and she started spinning. I went into the BIOS again and monitored the health and the cpu temp lowered to the normal range of 112-118F. For laughs I hooked up the rear chassis fan to the cpu fan lead and she spun up too. I ultimately moved the cpu fan back to the normal leads and she spun fine again.

Ubuntu booted just fine after that.