I have been having this problem for some time now, at least 6 months (through various versions of Avast) up to and including 4.8.1201. I have rebuilt XP +SP3 from the ground up (starting with an MS slipstreamed XP build with SP3 included). I was having intermittent system hangs on booting (no response except for mouse cursor). I finally traced it down to the 1ASV4 service hanging the system. If I leave this service set to manual and manually start it after the system is stable, I have had no problems (so far). But if I leave the service as automatic, it randomly hangs the system.
Just set in the Troubleshooting page of avast settings to delay services start. Post back the results.
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