This is the problem with trying to convert pre-builts into gaming rigs. You'll need a full tower just to have a chance of even fitting any decent video card, but the PSU's rarely supply very much more power than is needed to run the system in it's stock configuration, so a powerful video card won't work because you won't have the voltage or the PCIe connectors required to run it, and you can't just swap out the power supply for a better one because in pre-builts, they are almost always going to be proprietary, and a proprietary PSU with the wattage that you would need is almost never an option. This class of machine will also typically only come with only 1 or 2 RAM slots, limiting your ability to upgrade that, as well. CPU coolers and case fans are also very basic in these machines, and aren't always upgradeable. If you start making mods that generate a lot of additional heat, the cooling that comes with it may no longer be sufficient, and also not be easily upgradeable, due to case constraints. Even upgrading to a better CPU on the same socket may not be possible, if the BIOS doesn't support any CPU other than what the machine shipped with. They really go out of their way to make sure that you will be buying a higher profit gaming machine for gaming, and not buying one their cheaper business class machines and upgrading it to the moon.