By default the windows server 2008 core comes with a dummy product key that you must change before 28 days or so.
To change the product key run this command
start /w slmgr.vbs -ipk ABCDE-FGHIJ-KLMNO-PQRST-UVWXY
where ABCDE-FGHIJ-KLMNO-PQRST-UVWXY is your product key
To activate the product key run
start /w slmgr.vbs -ato
to check the license and the activation state you have run this
start /w slmgr.vbs -dli
found this useful information in this site:
Hi, I wanted to make sure you got the latest product report. Did Roddy get it to you?