password and username

You don't give much to go by, but if you're being prompted for a password, this is the OS, not Flash Player prompting for the password.  See the What userid & password do I need to install Flash Player?  FAQ for more information.  If you don't have a password, you leave the field blank and click OK to continue.  If you've forgotten your password there are links in the FAQ to other sites for assistance with resetting the password.