Log on problems

I just recently updated my Norton Antivirus software - and just this morning,
I tried to log on to my computer (which I don't THINK I ever had a password
for) and as the administrator of the computer (it's a home computer) it asks
me for a password (which I thought I disabled) and it has locked me out of my
own computer!! How do I rectify this????? HELP!!! (thanks!))