After clean installs of 5.0 from the first full release version, through a number of updates, I updated from the last prerelease version 5.0.460 to release 5.0.462 via the update program option within 5.0.460, instead of doing yet another clean install.
It seemed to work fine (including a number of both hot and cold reboots, and also at least one hibernate) up until this morning, when at bootup the PC would not progress past the opening screen XP screen with the moving horizontal bar. It froze just after the point where the USB mouse and keyboard are enabled.
A repeated bootup and also a boot to last working configuration did not solve problem, however I could boot into safe mode. As low voltage on the +12v rail can cause freezing during bootup, I removed the covers and checked both the 12v1 and 12v2 rails from start of bootup up until the freeze. (Fluke digital multimeter).
Both rails were around 12.13v and stable from turn on to the point where the freeze occurred.
As the last software that had changed was the Avast update, I uninstalled it from safe mode. The computer then booted normally. I have since done a full clean out of Avast, including running the Avast 5 clean up tool, rebooted and done a clean reinstall of 5.0.462. Touch wood it's all working OK at the moment.
Of course it may not have been caused by Avast, but one has to be a bit suspicious.
For those who may wish to ask, this PC has never had any other AV system than Avast. It started life with Avast 4 series and that was removed with the clean up tool after the first abortive attempt to update directly to version 5.
Edit: Additional information. Full scans with Avast, Malwarebytes and Superantispyware have given the PC a clean bill of health. This PC in fact has never seen a virus or malware (other than EICAR used in testing Avast). There were no files in the virus chest.
