Your problem might be related to the stepping code of the CPU. You may have to update your M/B BIOS as well to adjust the stepping of the new CPU.
For example: your previous CPU stepping code is C0 and your new CPU stepping code is E0. Your BIOS may support C0 stepping code but not E0 stepping code. Therefore, you need to update BIOS.
Another example: My Gigabyte M/B has a new micro code update. But I do not need it now because my current CPU microcode is O.K. But future CPU changes may need that update.
Hope the above helps.