If you have a PCIe x16 slot, then you can use a PCIe graphics card, but your power supply unit probably can't handle much of a graphics card upgrade. Do you know your power supply's specifications? If not, then you can check by looking at the sticker on a side of the PSU. The total wattage is important, but the 12v amperage is more important. HP is known to use weak power supplies and you'll probably need to upgrade your power supply before you upgrade your graphics.