Q: I forgot my password for iMac and don´t know how to iniciate it. I don´t have the CD to do it....

Resetting or changing a password:

For Snow Leopard or earlier:  http://support.apple.com/kb/HT1274

For Lion or later:  http://support.apple.com/kb/HT6022

This is also useful:

http://www.macworld.co.uk/ipad-iphone/news/?newsid=3463233&olo=email

If it's running Mac OS X 10.6.8 or earlier, insert a Mac OS X install DVD, restart with the Option key held down, click on it, and use the Reset Password utility.

If it's running Mac OS X 10.7 or newer, restart with the Command and R keys held down, open the Terminal, and use the resetpassword command:

https://discussions.apple.com/docs/DOC-4101

If you are in the US call Apple Customer Support 1-800-767-2775, provide the Serial Number and specifications of the Mac, and for a reasonable fee, they will supply a replacement set of system discs (if available).

The discs will be for the original version of the OS that was pre-installed when the Mac was manufactured.

If you are in another country:

http://support.apple.com/kb/HE57

If you are running Lion or Mountain Lion you won’t have been given disks. Instead you use the recovery partition or internet recovery:

http://support.apple.com/kb/HT4718