Windows Vista Need Windows user name and password??

My antivirus has a problem, so a message tells me. When I checked for resolustion to them problem windows found one and needed to down load a newer version?, when tried to down load was asked for user name and password?? Thats how I came to be here, in another site it prompted me to register for (username and password?????). It was for this site not to able me to down load updates??? I guess you can tell I dont know much about PC's. Thanks so much. Laura

 

What AV are you using? Paid or Free? Is it up to date? All AV's have a way that you can manually check for updates.