I strongly suspect that OnlineArmor (admittedly not long for this world since support for it ceases in early 2016) can cause problems when installing or updating Avast to version 2015 R3 (2015.10.3.2223). I found that by disabling OA’s Web Shield and Key Logger protection, Windows XP no longer locked up. The remaining OA features cause no problems and the new Avast works very well.
Yup, running OnLineArmor with AVAST 2015 R3 causes strange things to happen. Removing OnlineArmor is the only remedy. After that, the problems simply vanish.
That explains why OA took so long to start - doubled boot time and soaked up more RAM.
Uninstalled OA and installed Comodo Firewall and now it seems OK.
Be good if this were to be fixed, by Avast or OA, as OA is a bit lighter and quicker than Comodo.
If support is going to be ending for OA then why bother using it…just move to something better and stop wasting time on something OA developers can no longer be bothered with either 