Well, after you ticked msconfig but why did you do that, you ought to have removed the tick all together so the OS would automatically check. Anyways, how many cores does the Task Manager show.
Did you delete the CPUz INI file and then rerun it and check?
It's an i3 ....... what 4 cores are you talking about?
He was probably assuming i3 is quad core, since Core 2 ended up with 4-cores and there's no logical reason to assume i3 would be less cores. You would have to know that i3 is simply re-branded Core 2 Duo in order to know that i3 is only two cores, and that's not really ultra-common knowledge. In fact, it's pretty stupid on Intel's part.
However the situation doesn't change based on his error - make sure all (or, for technicality sake, BOTH) of your cores are enabled in the BIOS