Changing CPU from a socket to another

Hello everyone , 

Hope you can give me some help with a poweredge 2900 having 2 CUP's sockets but Only 1 CPU , the 1st socket is OFF the server boot but nothing happen , i changed the CPU to socket 2 , the server boot but it halt with the messg : "change CPU from socket CPU 2 to socket  CPU1  " , 

I think there's some config to do but i can't enter system setup when i press F2 , it actually write " entering setup " but the system halt with the message above 

Can pls someone give me a hint :)

Thank you