Actually, what kind of CPU -do- you have? If it is AMD, then you got one of the X3 Phenoms, not an X4. Instead of trashing the Phenoms that had one core come in under minimum, they decided to cut the links to the substandard core and sell them as a value chip; the packaging remains identical, only the part number is different. 

And there have been times when those X3's have been remarked and sold as the X4 Phenom.

Now, if that is an Intel chip, then you just have one core that has died on you.