Core 2 quad is showing 3 logical processor

Try these.

Go to msconfig. go to the boot tab. go to advanced. make sure that the box called number of processors is not checked. if it isn't checked, click on the dropdown menu and click on the number 4. reboot.

Go to the device manager and click on the arrow beside processors. how many are there?

If none of that works, can you give us a printscreen of your taskmanager performance tab and the device manager?