Doesnt sound good... Did you possibly damage the motherboard though this process by not handling the components in a static-free environment or ground yourself before working on this. A friend of mine blew his motherboard when he was swapping Ram and had a spark leap from his finger to a ram stick.
Also did you apply new thermal compound to the new CPU top before locking the fan/heatsink down to create thermal bond and avoid cooking the processor due to the lack of a thermal bond. Simply placing the heat sink from one CPU to the other is not enough, and can cause to cooked CPU and blown motherboard.
Did you swap the CPU and not move anything else around, or did you completely remove the motherboard from the case and then install it back after?