You need to have SLIC 2.1 in bios + certificate and serial this machine came with vista so it will have SLIC 2.0 so you either need to get modded bios or use say DAZ loader and RemoveWAT.
Also I suggest you better try another Ultimate Key since it's an blacklisted Dell Key(not sure)... And try to validate your key..
Well he could at least try HP Ultimate key, i missed the fact it was dell also the is Not Blacklisted.
I am preety sure that the HP Compaq 6720s has SLIC 2 in the bios and not SLIC 2.1. I think the bios in the HP Compaq 6720s is unmodable. Urie post above seems the best advice. Kind Regards bp1
But few days ago someone posted a official response from a M$ employee saying both Dell & lenova keys are blacklisted.. However in practically it is not still
I still don't believe those things have you ever thought what would happen every dell machine bought with Ultimate comming up as not genuine, they would need to send out new install dvd's to every one and i have checked dell site Ultimate is availabe. also i think the levono key was leaked long while before dell.