thaks to all i've made it (i use Windows XP home edition)
i used a online scanner (i've had 200 viruses !!!) and i repair all the files. the i install avast and it works! thx to all
Well I thought you had some problems but 200 viruses.
Glad we could help, welcome to the forums.
You didn't answer the question about a firewall as I suspect you either don't have one or you have the XP firewall (assuming your XP home is up to date SP2), which doesn't provide any outbound protection.
Whilst the windows XP firewall is usually good at keeping your ports stealthed (hidden) it provides no outbound protection and you should consider a third party firewall.
Any malware that manages to get past your defences will have free reign to connect to the internet to either download more of the same, pass your personal data (sensitive or otherwise, user names, passwords, keylogger retrieved data, etc.) or open a backdoor to your computer, so outbound protection is essential. Otherwise keeping your system clean will be a continuing battle.