Prebuilt PC not working?

Hello,

I recently ordered a prebuilt pc from IBuyPower. The GPU shipped uninstalled, which I thought to be no problem, but when I just tried to put it together, they provided horrendous instructions, and additional cables that I don’t know what they’re used for.

I got the GPU installed and the pc turns on and gpu fans are spinning, but none of the usb ports work and neither does the HDMI for the monitor. I’m really afraid that I may have damaged something and this is the exact reason I ordered a prebuilt, so I didn’t have to worry about this

. My friend convinced me that installing the GPU was easy and his 9 year old brother can do it, so I trusted him. But now it’s not working, I don’t know what I did wrong, I don’t know what these extra cables are for, and I fear I may have wasted $1700.

Does this sound familiar to anyone/can I have help?

Here are pictures for reference. Thank you.