cpu had been changed message on Fujitsu siemens esprimo edition P2511

Hi I have this message appear on the Bios screen 'cpu had been changed message on Fujitsu Siemens Esprimo edition P2511'

battery has been tested and is good, have removed the processor cleaned it and re applied thermal paste on it but is still the same, have also reseated and clean all push on fittings inside and used compressed air to clean all dust etc, could it be a processor problem ? time and date need to fixed in the Bios at times and also the Pc does shut down itself at times, this usually happens shortly after booting up, have tried to get a reading from cpu using speed fan but for some reason it only gives me Hard drive reading normal at 27 C, have also restored defaults in the Bios, any ideas please  

Replaced the battery but still same result

The error message comes up every time the Pc comes on, and yes I did hit the F1 key to continue and it then boots up into XP as normal each time, the  F2 key will get me into the Bios so all is ok there    

Strange now it powers up but black screen it wont power the monitor and it won't even power off with the button  

Thanks qhn will try that tomorrow, sorry for the late reply

Ok now booting up again think the power button is a tad faulty, have to keep it pressed for a while while powering up,still same error message ''CPU had been changed'' at boot re did all cables still same, starnge this was fine until i re did the thermal paste on the processor even did it secondly but still the same error, by pressing F1 you can get into windows ok or F2 for Bios settings

Was going to have another go at that this morning too, will let you know how it goes 

Have given up on this one but thanks for your help