If so, go to this link:
I'm hoping you remember your Security questions! If you don't remember those, then I hope you have a rescue email.....(if you have one, it will show as a link at the bottom of the security questions you can't remember).
If you don't have a rescue email....then you will have to contact Apple Support - that is the only way to fix it if you have exhausted the options above.....
Do you mean that the Flash install is asking for your admin password and you forgot it? It's the same password that you use to log into your computer - is that what you've forgotten? Try this - http://support.apple.com/kb/HT1274.