E74 Xbox 360 System Error?

So yesterday, I was playing on my Xbox when suddenly the screen goes black and I get this error stuff in many languages. I’ve tried many things to resolve this problem.

I turned the console off.
Unpluged all the power and AV cables from the console.
Unpluged the power cord from the wall socket.
Firmly reconnected all the cables.
Turned on the console.
Error still appeared.

I also tried to let the Xbox cool for a long time and replugged the accessories still error came up.

My Xbox is always ventilated so it has air easily coming through out its fan.

I already called 1-800-4my-xbox and the box to send the xbox to them is going to come next week. Lucky for me, my warranty was still valid so there’s no problem about the money.

I tried to only plug in all the accessories besides the A/V cords and then the light wasn’t flashing on the Xbox but of course I couldn’t see anything without it plugged in. So I think maybe there may be wrong with the A/V cords but I’m not sure, if there is where can I buy a new one?

I need some suggestions and I’ll really appreciate them.
Sorry for the long letter.

Thanks for your support and happy holidays!