I’ve just had a very similar problem with my XP system. I checked for free avast updates and it said one was available, so I clicked the button. It appeared to download and install OK, then said it needed to restart my computer to complete the process. I clicked OK to give it permission. WinPatrol reported that a one-off program would run on restart which I definitely accepted. When the computer restarted and I logged in, the screen just displayed the background, no taskbar, no icons. Nothing appeared to be happening. There was no hard disc activity. I waited nearly 10 minutes and then decided to do a forced manual shutdown ie. I had use the on/off power button.

When I too nervously rebooted the system everything worked normally.

I too had visions of a totally crashed computer and I’ll be very reluctant to update my free avast again in future.

Dell Dimension 4400 / Pentium 4 2GHz / 512mb RAM / 40GB HD Samsung CDRW/DVD / 64MB NVIDIA GeForce2 /
Win XP Home SP3 / XP Firewall / Avast (Free) / WinPatrol+ / MBAM (Free) / Win MSRT / DropMyRights / IE8 / Firefox (AdBlockPlus / DoNotTrackPlus / WOT) / BT Home Hub 3 (wireless)