A recent problem (January 2005) with a ZoneAlarm update (and maybe an XP update depending upon which forums you choose to believe) can manifest itself exactly like that.
Solution that worked on my sister's laptop was to:
- download the latest ZoneAlarm setup kit from ZoneLabs
- disconnect from the internet
- uninstall existing ZoneAlarm and reboot
- reinstall new ZoneAlarm and reboot
- reconnect to the internet
Would recommend that you try the same if your setup is XP / ZoneAlarm / AVG.
RC