Internet Security, 5 Pro, 5 Free failures to update

Hi: Bought Internet Security and it installed but it wouldn’t update. It gets to saving packages and get an “Invalid file signature” message or is get a blue screen saying “IRQL not less than or equal” and it reboots before I can read any more. Uninstalled and tried 5 Pro - same result. Tried 5 Free - same result. Downloaded 5 Cleaner and ran it. Downloaded 4.8 Home, it installed and would not update. Same as before, blue screen.
Before I did any of this I had a working 4.8 Pro.
Any ideas please? I’ve sent about five requests to Tech Support but unlike the old days they don’t seem to work weekends. There seems to be a lot in the Knowledgebase about problems with 5, has Avast screwed up like McAfee did?
It seems that you can send the dump file to Avast at ftp://ftp.avast.com/incoming. Does one use something like FileZilla to do this? Instructions aren’t clear to me.
Anyway, stuck here with no antivirus.
Thanks.
Donald

Oh! I should have said that I’m using XP Pro SP 3 and up to date.
Donald

Please send me a couple of the latest minidumps (\Windows\Minidump folder) to kurtin@avast.com. Thanks.