Dell precion T5600 not start after adding a cpu2

Hello I have this dell T5600 with one CPU on CPU1, H've bought a new CPU which is as same as the old CPU on CPU1 socket, but When I add a new CPU on CPU2, the PC not starts. I've tried to put the new CPU on CPU1 without the CPU on CPU2 and the PC starts, I've tried also to put the old CPU on CPU2, the PC not starts. therefore when there is the CPU (the old or the new which are same) on CPU2, the PC not start. I need help please. Here is my configuration: CPU, both are Intel Xeon E5-2630 2.3Ghz, the power supply is 825W PSU. The problem looks like the socket CPU2 don't work and i'm not sure. I really need help please. Thank you in advance. Regards