Why my windows missing 2 or 3 cores if I have I7? VAIO F 12

I have Sony F12 (VPCF126FM) WITH QUAD CORE I7 Processor. But Task manager shows only 2 cores! CPU-Z shows that I have 1 core with 2 threads! After I changed BIOS Windows Experience Index on my Processor start showing 5.3 instead 7.1 before (but in both ways it was shown 2 cores in task manager) I have Windows 7. Resource monitor shows cpu0 and cpu1 (2 cpus only).
HELP PLEASE!!!

 

I SOLVED THIS PROBLEM MYSELF (Thanks to google)

I got only 2 threads instead 8. 1 core was always overbooting using Turboboost and temperature was high. I made my comp use all cores.
This may be because of wrong booting windows (Win 7 in my case)
Do this!
Start/run/tape "msconfig"/push Enter/ the window will be opened. Boot/ advanced settings/do not choose any # of cores (I mean make the number "1" or "2" GREY). Then apply and reboot
THAT IS ALL!!! The same for Vista!
By specifying 1, you tell the computer to ignore the rest of the remaining cores.
By NOT specifying anything, you tell the computer to use it as it should be.
It helped me. But may be there are another problems (like half-dead processor etc)