The exact same thing just happened to me. I logged on here to report the problem.
I an using IE8 and I have my home page set to go to a blank screen. IE8 worked fine up until today when I installed Avast 8 and I went into the Settings > Browser Integration and installed the Ad Blocker. My IE8 froze each time I tried to open it up - tried 3-4 times - but as soon as I went back into Avast and uninstalled the Ad Blocker, IE8 started working just fine once again.
Correction: IE8 still freezes when I try to open it. It didn’t do this until I installed Avast 8 earlier today. I’m going to see if I can find a link to d/l an older version of Avast and wait until they get the bugs worked out with the new one before installing it again.