Hi people, I just wanted to provide my own input here,
This black screen problem just happened to me today, first time, and I have no firewall other than the basic windows one. But what I do have, is that, at work, I am behind a proxy, and at home, I don't have a proxy, and I use the same laptop in both cases. Which means I keep changing my configuration all the time. And usually, to make things faster, I only change it in the browser (Firefox 27.0.1), not in the system internet options, because I'm lazy.
What it does, is that I often see programs, happy to take things in their own hands and wanting to update something at startup (which means - download at startup and then update, let's be precise for once), and of course, they fail, because they did not let me a few seconds to change these d*mn internet settings, so they can't access the internet, although they do see a network connection!
And I think this is what happened today, and as I did not know how to invoke the internet settings from the command line from the windows 7 x64 task manager, I just rebooted while cutting all physical connections from my computer. Then, avast understood it could not update, and let me start my system normally...at least I think this is what actually happened.
And what is said elsewhere in this forum about "if this functionality was not present, avast would crash irremediably, as we [avast] won't be able to fix it from our side". I never seen avast crash irremediably before...so I wonder, what is actually the core reason for having such a buggy service running at startup.
That's all I wanted to say!