Hi

. . . . what is computer id definition im being ask to fill in field but want to know what to put there . . .

The computer ID is a code generated when you opt to register by Email or Telephone in the start up registration dialog.  When you get the registration page there should be an option (lower left IIRC) in the dialogue to register offline.

Selecting this will then take you to a page where you can generate the computer id which is then used by Magix to generate your serial number.  Instructions on what to do are in the dialog.

HTH

John EB