I've [rudely] discovered within the last two days, that Avast does not allow Internet Explorer to open on 64 bit systems.
You get nothing but blank pages. I had to open IE in (no plug-ins) mode, go into the Manage Add-ons, and disable the Avast 32 bit protection ONLY, leaving the 64 bit protection on. Once I've done that, I can then open the 64 bit Internet Explorer.
Took me some time to figure out that it was actually the Avast plug-ins.
Avast needs to fix this issue. I haven't tried opening up the 32 bit IE, but why should I if I have 64 bit?