Why is my Xbox Slow?

Just bought a used Xbox one s, It worked fine but now it’s really slow, got the green screen of death and did all the usual resets and cleared the system twice, but is very very slow takes around 10 minutes to load up, and games take around the same to work, which they rarely boot up, but when they do they work fine. I have an external hard drive and was thinking maybe that’s what shorted the xbox’s internal? I unplugged it to be safe but i’m just not sure what I need to replace here, thanks for any answers!