How many i3 processors do you have? Or are you refering to all of the cores? If the latter and are using Win7, press CTRL-ALT-DEL and go to Task Manager/Performance. You will be shown a graph of cores.
Once you see the graph start running some programs.
If you have hyperthreading turned on in the bios you will see 4 cores, just remember two of them are hyperthreads and not true cores, otherwise you will only see 2 cores.