Freezes

[Maxsphere]

I am a newbie here.
Problem is using on off button system loads Avast freezes and goes no further for interminable time. Cannot use the ctrl-alt-del route to retart or shutdown  must use power of. This is happening 9 times out of 10.  Today because of this the program was un-installed and then re-installed. Using XP Home , intel p4 @ 2 Ghz
120Gb HD , explorer and other browsers available.  Active startup is Zone alert firewall, Adsubtract ad blocker and  intermute corp Spysbtract.
ANY HELP?

[Staind]

Have you installed on your system, previously, Norton Antivirus or other anti virus software? If so, which ones?

[Lisandro]

Did you add other Windows updates? There were some about shutting down.

Can you try to repair your installation?
Go to Control Panel > Add/Remove programs > avast! antivirus > Remove
Then choose Repair function in the popup window (Repair).

If this does not succeed, can you try to uninstall ZoneAlarm and see what you get?