You need to find out if the unit is leased (it probably is). If it is leased you will not be able to activate it and the person that deactivated will be charged for the full amount of the unit if it is not returned to DIRECTV.
If it is a owned unit you will be able to activate it but you will probably need to buy a new access card from DIRECTV for $20.
If it is a owned unit you will be able to activate it but you will probably need to buy a new access card from DIRECTV for $20.