I'm afraid you are asking the impossible, even if you already have SUITABLE case, hard drive, and PSU (knowing exactly what they were might help). The i5-3570K is unlocked processor, for overclocking. Just the CPU, cooler for it, and a reasonable overclocking motherboard, would set you back, effectively £300. That's without a graphics card. Even a fairly minimal GPU, for modern games, at good resolution, you really need to be thinking around £100, or more. Then you need, presumably, an optical drive. Have you got the peripherals, like keyboard, mouse, monitor, and operating system. You either need to substantially increase budget (how much depends if you already have "peripherals"), or you need to accept something a lot less than i5 (might even be impossible then, if you need peripherals). If you have monitor, we do need to know its resolution, to know what would be adequate, for it.