Perhaps you didn't reinstall Windows when you set up this computer? My guess is that Windows is loaded with its uniprocessor CPU setup instead of its multiprocessor CPU setup. If so, try a repair install.
that would be guse too but if not do this. click run, Type MSconfig, click boot option tab, & click advanced options uncheck number of processors. Then reboot and see if this fixes your problem. And it is not a XP it is an X2. You might want to change your topic title.
thx for answer
in msconfig numproc section i can choose only one number and that is 1 ( i havent2) it is already unchecked.
second answer amd patch for xp hot fix i already instal but my problem still going
i have xp sp3 full updated and also updated manual updates too.
but my problem still continue.
i have newer change my cpu or harddisk to another computer.
and i also now wat is computer. i didnt noob. i am using and fixing computer or programs problem. that is i havent solved first or second problem.
Not sure about the X2's, if they do this or not, but it solved my disappearing core problem.
If you have Cool and Quiet enabled, it may shut down the cores not being used, and also lower the core speed of your CPU if it is not needed.
I noticed this with my PII 920, after a while if I was doing something simple and brought up the task manager, I noticed only 2 cores at times, and only 1 core at other times. Turn off Cool and Quiet and see what happens.
If that does not work, try simply deleting the processor from device manager, and let Windows reinstall it when it reboots.
Cool and Quiet also seems to never let your CPU run at full speed. With it enabled, my 3D mark 06 score was about 8500.
Turn it off, and I get over 15,000. Big, big, big difference.