I Installed again the windows XP, I installed avast! home in the latest version, I installed the SP2 and in the security center it says the avast! antivirus isn’t active.
When I go the acces scanner panel there are all the scaners except the “normal” scanner.
sorry if the english is bad, but i have the spanish version and I don’t know some of the names in English.
Try to go to the control panel > add remove programs > check avast and look for repair feature. Be sure that all needed providers are checked with tick. You must be online as i know, if you want to use it. Also you can to try re-install avast. Another question - maybe somethig is said in the avast log about this? (right click on -a- ball > avast log viewer)
Answers for XP Security Center not detecting anti-virus program could be found here: http://support.microsoft.com/kb/883792 (the link was kindly found by David…).
when i reinstall it doesn’t appear the resident scanner, only the other ones.
ok
I uninstalled it and installed the English version
now it works ok
thank you 
Do you have any other antivirus in your system?
Do you use any anti-spyware or startup monitor (TeaTimer, Ad-watch, PrevX, ProcessGuard, etc.)?