Avast is sudden;y performing differently

I’m running XP home SP3 on an MSI SLI config. I’ve been using Avast for years and installed latest version of home free on this rig. Last week it started freezing on the desktop - soft reboot usually fixed it, but that’s a pain. After some removal of other software and last known boots, I noticed that the tray icon has a yellow triangle w/! in it - when I right-clicked it, it showed me it was waiting to be registered - it never notified me of this, never popped up or anything. It had also somehow shut off real time protection! I registered, I turned on real time, but still on first boot, it freezes with the yellow exclamation. I am confident the rest of the system is healthy, I’ve defragged and run a background defragger, I’ve chkdsk’d, all my software and drivers are up to date, the drives are fairly new, and the system has 4GB of matched memory and is a Phenom II, so there’s plenty of power and space and memory; there are no power issues with an 800 watt PS. I don’t understand why a cold boot fails and a second warm boot succeeds.
I am also running Ashampoo’s Professional Firewall and magic defrag3, and Nvidia desktop, but on boot that’s all that’s loading along with all of MS’s files.

The system is right up to date - in fact there’s an MS update in the tray right now. I’m at a loss as to the cause - any help here? Thanks,
promytius

I suggest an installation from scratch:

  1. Download the latest version of avast! Uninstall Utility and save it.
  2. Download the latest avast! version and save it.
  3. Uninstall avast from Control Panel (if possible). If, for any reason, you can’t run it, try booting in Safe Mode and doing it from there. Anyway, boot after that.
  4. Run the avast! Uninstall Utility saved on 1. If, for any reason, you can’t run it, try booting in Safe Mode and doing it from there. Anyway, boot after you’ve run it.
  5. Install avast! using the setup saved on 2. Boot.
  6. Register your free copy or add the license key for Pro.
  7. Check and post the results.