Help with an RX 5700xt

[Ubuntubr]

So I recently bought a new pc and was going to start gaming, but I had a few issues. I bought a Crosshair hero 8, 16gbs of ram and an Rx5700 xt Strix. My cousin was going to give me a CPU so I did not bother looking for one. When he got to my house he had a R5 1400 processor which is not compatible with the MB. So to not go to a complete waste until the other CPU arrives, I thought why not put it in my old system(when I say old I mean Old). I get a black screen on boot to windows every time. After looking on some forums I found a way to boot. I need to make the PC boot using the internal GPU and use the rx5700xt as the gaming gpu. But there's a problem. Games are pretty lagy and it's not only the processor bottlenecking the card. When I open up a game the GPU clock and vram don't ramp up to the target and I get lots of FPS drops. Can someone help me? 

Old system specs:
CPU: FX 8320E
MB: Asus M5A78L-M / USB3
MEM: 8GB corsair DDR3
PSU: EVGA 600b bronze

[WhitetailAni]

Just now, Ubuntubr said:

my old system(when I say old I mean Old)

That's not old.

My 1999 Power Mac G4 is old.

Also, your CPU might not be compatible with your GPU (not sure if that's how it works though).

See if you can get a 3600, 5600X or 3700X, or 5800X.