I forgot the PIN number of my iMac
Welcome to the Apple Support Communities
What are you referring to with PIN number of your computer?
Do you mean your Administrator password? Which operating system are you using OS X 10.6/10.7/10.8, or something else?
Hi mende1 - I'm not following you round, honest
If it is a BOOT Pin, IE it won't boot without entering a Pin code, you need to take the system to an Apple store. They are the only one that can help you.
If the "PIN" number you're referring to is your AppleID password, here's where you need to go:
Retrieving data ...