Same problem here as mentioned. Running Win Vista 32 all updates current, Dell Inspiron 1525 laptop, 4G RAM and dual core Intel 1.87 GHz processor, no hardware virtualization available.
I purchased AVAST 2015, latest version a couple of days ago and Chrome, Firefox and MSIE 9 all freeze. Chrome seems to run the longest but after a minute or two will freeze. Firefox is hopeless in the AVAST sandbox. I can't even start browsing before it locks tight. Additionally closing the browser and attempting to re-open doesn't work. I've got to reboot to be able to use a browser. Tried the fixes mentioned in the posts above without any luck.