a clock speed (cpu speed) error isn't something you see too often. Is this a custom PC?
there are 2 possible methods to changing the clock speed (overclocking) on your CPU.
One is through the BIOS and the other is through jumper pins on your motherboard. Not all motherboards support this feature and the one's that do usually support only 1 or the other.
for the reasons you're experiencing right now, overclocking your processor is not recommended.
Enter your bios and try to lower your cpu speeds if the option is available. To enter your BIOS, you press a certain key on your keyboard immediately upon reboot. The time to press the key is before any windows logo shows up, if you see the windows XP logo, you're too late. Restart the computer and try again. The particular key to press is different depending on which BIOS you have. Usually the keys that are used are:
Delete or F2 or Esc
Search around through the options and find that setting to change it.

I forgot to add that prior to the bios error message, just seconds after the ON switch is enabled, one of the two fans (possibly cpu fan because the P/S fan was recently replaced ) makes a terrible
bearing noise. After 3 - 4 boot-up attempts all is fine. I also notice that the BIOS CPU speed is set correctly to the CPU spec of 2.4 GHz

It may be the processor fan still. the timing of the processor fan is cpu controlled, if it has trouble spinning, the cpu usually throws errors (though they usually say there is a processor fan issue) the chasis fan doesn't have such a check on it.
Spray the hell out of the cpu fan with WD40 (you probably should detach the fan and spray into the bearings) and try it again.

Thank you, I'll try your WD40 suggestion first.

Sorry for the delay. In the end I did not lubricate the cpu fan. The reason: In the back of my mind I recalled that if I waited at least 10 minutes (happened on rare occasions) from the time I enabled the power bar to the time I enabled the computer switch the boot-up was fine. So I did some validation tests at least 10 out of 10 times a) using the delay and b) using no delay. The results: The delay worked fine every time and no delay led to bearing noise and the bios error every time.
So I don't think the cpu fan is the problem. The cause is still a mystery and it could get worse but the 10 minutes lag time is bearable for now. Still, as an engineer, I would like an answer. Any more ideas?

power bar?
is the computer on a power tap such that you essentially unplug the maching when you turn off the computer? Like the plug strip has an on/off switch? If so, several of the components, specifically the capacitors need some time to build charge, otherwise you get underpowered behavior especially on SOYO boards. it's like those old-fashioned TV that take a few minutes to warm up and deliver a clear picture. Currently, CRT screens stay plugged in and continuously draw power to keep the emitter warm so you get a much quicker picture displayed. essentially, some motherboards need the same continuous power flow. it uses as much as a small alarm clock in terms of power usage.

Yes, it is on a switched power bar along with 5 peripherals. It had occured to me that there might be a leaky cap because because this problem didn't exist for a coiple of years. But you may be right about my motherboard needing to be left on, so I accept your solution. I'll put the computer on an unswitched cord.
Thak you kindly for your good advice oracleofDelphi.