Any reason why you use a way outdated version..!??
I stuck with AVAST 7.0.1474 because I did not like the changed GUI's nor added bloat that has continued to be added to AVAST ever since. I tried v8 long ago and disliked it, going back to v7 and have kept it ever since.
But the other day after updating W7 to SP1, AVAST v7 created a boot time of 4min. I verified it was AVAST doing this through event viewer and MSCONFIG selective startup. Uninstalled/cleaned reinstalled v7 with a 2min startup, still unacceptable. This is with only File and Web shields installed, no cloud svc, and no auto-update of program (but db, yes).
So uninstalled/cleaned (using AVAST tools in SafeMode, yadda yadda) and tried the newest AVAST 2015 beta 10.something. Booted in 1:15 min, but the machine remained unusable for the next 2 min while AVAST hogged resources. (And again, only installed File & Web shields. No cloud, no streaming updates, no sft updater or other tools or shields.)
I am not interested in having AVAST start up after the other services as that impacts its effectiveness, but I tried it just to see if it would make a diff in boot time, or in any other way. It did not make any appreciable diff.
On top of this, I don't like the whole Win 8 GUI everyone is going to, as if Win 8 is any good or has any kind of rep for being easy to navigate and nice looking.
So if I can't get v7 to work with SP1, it's reluctantly off to a different AV. Which it looks like I might as well do since you are saying AVAST will not support older versions. I find this hard to believe. The virus db updates should work into perpetuity, as there will always be people who prefer the older versions for their own reasons. Newer is not always better. Far from it. And not just with AVAST.
PS I have no other startup programs but Comodo, the AV and Stickies. And without AVAST boot is 42 sec's.