Look in the BIOS for
CPU Unlock setting and enabled it, Save and exit the BIOS.
At first it may seem to be not working but reboot it a few time and it should find all 4 cores and show CPU core 0 to 4 are enabled.
How much memory does it have? what operating system are you using 32bit or 64 bit as windows can only use 4G in a 32bit system.