No picture yet i can hear sound green effect before it happend
First thing would be to make sure that you're only using the yellow, red, and white cables, but seeing as how you said you had picture before, I'm guessing that's not the problem. The 360 uses an automatic recognition for the hardware to make sure that it is set to the right input. So, in essence, it won't be that the settings were changed. I would say go pick up a new cable and see if that's the problem, it sounds like it is. If the cable doesn't solve it then I would say it's time to call Microsoft. For the guest with nothing working, call up Microsoft, I really don't know what else the problem could be except for hardware.