Avast is locking up PC on startup

Our Windows XP machine started locking upon the restart at the end of the Avast install. All subsequent restarts, warm and cold, have locked up as well. The boot sequence does not make it to the desktop, so there is no access to the start button, etc. What do you suggest for next steps?

Hi,

Will it boot into ‘safe mode’?

Will be trying safe mode at first opportunity tomorrow…

OK, do you have any other AV software installed on the machine? Or isn’t it an IBM machine? Or don’t you have any other low-level system software installed (firewall, defrag, backup,…)