Edit what and play which games, because if it's "video" and "new", I'd have to recommend building a new computer from scratch. The GPU is ancient, the CPU is ancient, and thus correspondingly the motherboard is likely ancient.
To get quality gaming performance out of this computer, you'll need to replace at least the power supply and the GPU. To get quality video editing performance, you'll need to replace the power supply, motherboard, and CPU.
However, if you are, in fact, dead set on keeping this particular computer, I would recommend buying a 500W power supply (not the cheapest available either, preferably something modular just for the meaningful cable management) and a GTX 1050 or GTX 1050Ti, or comparable AMD card if you can find one. The graphics card is the singular greatest component in determining whether games will play well on your computer, with the exception of 2D games (GPU benefits aren't that noticeable there), CPU intensive games (like Minecraft can be), and RAM intensive games (haven't found anything besides Dwarf Fortress for that, but there you have it).
If you want to upgrade your GPU to something meaningful, I would 100% recommend also replacing the power supply. Low quality power supplies (like the ones prebuilt desktops tend to come with) are not things you want to play around with the specification limits on. 500W is probably all you'll need, especially if you go with a GTX 1050, but your current PSU looks to only be 375W.
However, your system is still running DDR2 RAM, which is ancient. Please, PLEASE consider building a brand new computer. You likely will get better performance out of $500 spent on brand new components and putting them all together than you will out of any easy tweaks of your current system.