Wrong cpu detected

Have just had a machine in with an AMD K6 2 500 cpu. Machine has been running with no faults for 9 months. On booting today, the cpu is reported as 250 mhz. Cpu is configured through bios (no jumpers or switches on board). There is also a corresponding slowdown in the machine. Changing settings in bios has no effect, haven't had the cover off yet (it was time to go home).
Any thoughts to kick me off in the morning, never come across this before.
Any help would be gratefully received.

check the cmos battery, a weak battery could cause problems with jumperless speed settings.

Thanks GHSTech,
Very good point, will try in the morning and let you know,

Best regards.

Booted the following day and everything was back to normal. Checked everything else I could think of and couldn't find any problems.
Changed battery anyway, and hope for the best!
Thanks again GHStech, let you know if it comes back.