I had the problem of the strange green pixels and HDMI not working properly, lack of sound etc. I've also had problems before with the screen suddenly going blank for a few seconds and then coming back on (particularly annoying in dark souls).

I have a feeling it might have something to do with the display discovery in the display settings. My problem with this was almost fixed by changing my screen resolution down to really low, 400x600 whatever, restart the console, then I switched display discovery off, sound fixed here, which allowed me to choose higher resolutions and I could then raise it to 1080i but not 1080p were it would get the green pixels thing again.

I realise it's not a total fix but better than a messed up screen and no sound. Hope this helps.