It is possible that an update to your graphics card has been misread by the Registry. You could try to reset the number of cores, and see if it updates correctly.
If you have checked the core options in Msconfig, uncheck them again.
There is a free download called Easybcd. It is available, also, on these pages somewhere. Install it and, in the Advanced options,select "Limit Windows to 0 CPUs. "Apply"
Now shutdown the computer (Not restart)
Restart and open the Tas manager. Under "View" - "CPU History" on the top menu, make sure you have selected "One graph per CPU"
This could cure the problem.