I ve been through a similar situation when i had bought my Q9450 after running E8400 on the same motherboard. The HAL did not update itself to detect 2 more cores, hence it was only showing 2 cores instead of 4 cores in all the possible places.

We need to manually force the HAL to detect the 2 cores by checking Detect HAL at startup/reboot.

Suprisingly, even a fresh reinstall of Windows will not rectify this problem. It needs to be done manually.

I know the OP had a bad proccy, but this is for other people who face similar issue and that they could try this as a last resort before getting the processor replaced

Hope this helps !