HP Pavilion 550 AMD A8 Quad-Core Desktops

Note: “65 watt external power supply.”
This is a laptop motherboard in a big, mostly empty, case. Limited expansion capability - that’s why they don’t show the back of the case.
That said, the HP 500-series gives good performance for what it is; but it is not and will never be a gaming box.
CPU performance is low-end Core i3 equivalent. Check passmark cpu benchmarks for the exact CPU model.