'cant save product key' == typically if the media is read only, like running from the cdrom.
The product is installable without a product key in trial version mode.
If you have been running and booting from the cdrom, and the trial has expired, a new full install needs to be done on a writable media.
The video posted above can have you going in 10 minutes.

wadeal -- I edited your profanity. We would appreciate you not using such in these forums.