I have an Asus P4C800 deluxe motherboard with 2.8ghz P4, Northwood CPU. Running Win2k pro.
I built this in 2003 and until recently has worked flawlessly. There are two unusual issues that I am trying to figure out.
1st…
The CPU is now idling very hot, usually at 60 degrees Celsius. It use to idle at between 36 to 44 degrees Celsius.
I checked the CPU fan…no problem. Running at 2400 rpms. I checked the heatsink for dust…none. I removed the heatsink and CPU and cleaned and re-applied thermal paste. Still runs hot. Q-fan is disabled. Power management is disabled. 4 four case fans, plus the two on my Antec power supply are operating normally. I can leave the case open and direct a small fan toward the CPU and motherboard and the temps only drop 2 or 3 degrees. I checked all the voltages. According to the Asus Probe program, all are in spec. Still it runs hot.

2nd …
Every once in a while, the CPU will boot up at ˝ speed (1.4ghz). If I go to the bios, it reports the CPU as running at 1.4. And yet all bios settings are correct. It also shows the same speed in Windows, using SisSandra and CPU-Z. If I turn the system off and reboot, it will still come back running 1.4. I have learned that when the system is running at ˝ speed to shut down for 30 minutes or longer and reboot. It will usually come back at the correct speed. I know that the P4 has a safety feature that will throttle back the CPU if it is getting dangerously hot, but it is not hot when it is booting up. Even the temps in the bios show that. Now when it runs at 2.8ghz, sometimes the temps will get to 68 degrees or hotter and it doesn’t throttle back. As I stated above, power management is disabled so that it won’t throttle back the CPU. I thought that maybe the CPU sensor is bad and miss reading the speed, so I did some real world speed test and my programs run ˝ as fast when the CPU is at 1.4 then when at 2.8ghz. So I know that the system is definitely throttled back when the CPU is being reported running at 1.4.

Has anyone had similar issues with either the Intel CPU or with this Asus motherboard?
Someone suggested that I may have bad capacitors. I was told to check for bulging caps. My un-trained eyes did not see anything unusual.
Someone else suggested that the motherboard battery may be getting bad…how could the battery cause this? None of the bios settings are changing and yet the CPU runs hot and sometimes it boots at a lower speed. As a matter of fact, when the CPU is at ˝ speed, I can go to the bios and overclock it to the max and I will see only a very modest improvement in speed…maybe 1.6ghz. So when the CPU does throttle back, nothing you can do will force it back to anything close to the rated speed. And yet, when it is running at normal speeds, I can only overclock a little over 10% to a little over 3.1ghz before it hangs.

Stumped.