Interesting. That should not happen. Is it possible for you to show us some printscreens of where you see you only have 2 cores aswell as a printscreen of CPU-Z (if you don't know what that is google cpu-z and download the program)?
4 cores should show up in task manager/cpu-z. If not I would check to see that the board is running a BIOS with support for your cpu. It may not be at the moment. If it is running a BIOS that officially supports it I would then look around the BIOS to see if there is a option to disable/enable cores. Make sure if that is there that its set properly.
I called Gigabyte and we did some trouble shooting:
1. We checked the BIOS version and it was up to date (for win 7).
2. Then we checked the Divice Manager --> Processors. And we could see all 4 cores
3. We checked the Task Manager and it only showed two cores.
4. The Msconfig --> Boot and it only showed two cores.
Gigabytes conclusion was that the problem is not the hardware or software related to the hardware, that it’s Win 7 that has a problem. I am using the trial version of Win7 so I guess that may be the problem. Gigabyte told me to try Win XP on same system.
Could it be that it is the OS that is the problem?