What to do when Windows7 detects only 2 cores of the procesor corei5?Help please!

[idata]

The day before yesterday I shutdown the system and it was running with the all 4 cores, and yesterday in the afternon when i turned on the system only detect 2 cores, also tools like everest, gadgets, taskadmin detect the same, only 2 cores, please help me, this is the first time i see this problem and it happend on my machine, it is am asus p7p55d-e lx with a intel core i5-760. 2.8ghz.8m. with a SERIAL NUMBER L102B706 35048583A1246 and sSpec SLBRP MALAY

I think that if the procesor is broken it wont turn on, but in this case it does and is fully operational but with only two cores.

also i should say that the latest thing that I do with the system that day was seing the advanced options under the boot menu options in the msconfig window´s utility

[AP16]

advanced options under the boot menu options in the msconfig window´s utility

There is an option to limit number of CPUs/Cores detected by OS there. Is it enabled? Also, you can try to boot from OS installation DVD, go into recovery - advanced - command prompt and make: bootrec.exe /rebuildbcd , to clean potentially incorrect OS boot configuration.