Question EOG Strix b550 Gaming power plugs.

[Satious]

So I got a Rog b550 strix wifi motherboardand I'm making a new pc with it. I had planned to use parts from an old prebuilt, graphics card, power supply, and Ram. But the power supply cant reach, and doesnt have enough plugs for both the 24 pin, and the 4 and 8 pin slots. are the 4 and 8 pin slots absolutely necessary? I plugged it in with jist the 24 pin and the Bios was red so I figure this might be one of the problems? This is my first time building a pc and I'm not super bright about technical things so sorry if this seems like a stupid question.

 

[rgd1101]

full system spec?
what the exact model of the prebuild and or the exact spec