Do you mean that you used the heatsink from the 850 CPU?
If so the it is possible that it is not good enough for the 1400 cpu
Another possible problem is that the 850 CPU is a 1.6v processor and the 1400 is a 1.5 volt processor. Depending on the settings it could be getting to many volts to the new processor.
Normally that little bit should not matter, but maybe the settings are wrong in the BIOS and that is why it is overheating.
What do the capacitors look like on the motherboard? If they are bulging or leaking then that could be why it is overheating as well.
If you don't know what caps are then go here
There are only so many reasons why it would overheat.
Bad thermal grease, fan not turning fast enough, heat sink dirty, wrong power to the CPU in the BIOS, caps or power supply or voltage regulators giving the wrong voltage.
Thats all I can think of right now.
Asus M4A79 Deluxe, Phenom II 940 BE, 20,770 3D06Asus Moderator
~ My CPU Overheating Guide