1066with phenom 955 not working ?

I assume this is the RAM you have:
KHX8500D2K2/4G 4GB DDR2 1066MHz Non-ECC CL5
(kit of 2 – 2GB) 5-5-5-15 2.2V

Note the 2.2V requirement. Your motherboard defaults to 1.8V supplied to DRAM slots. From the manual:
DDR2 Voltage Control
Allows you to set memory voltage.
Normal Supplies the memory voltage as required. (Default)
+0.1V ~ +0.3V Increases memory voltage by 0.1V to 0.3V at 0.1V increment.

So like my MB, the max voltage you can supply DRAM with is 2.1V. That may mean that your RAM won't ever run at 1066 - mine wouldn't and I had to return it and get some 1.8V RAM.

If you're currently only sending 1.8V - the BIOS setting is set to Auto - then it might work if you increase the increments. Try it at 2.1V and see if it POSTs as 1066. If it does, then try a lower setting. Don't worry about the dire warnings or red text in the BIOS when you increase the voltage for DDR.

Maybe your system running the old processor wasn't ever taxed by the processor. And this might also be related to the difference in an AM2+/AM3 processor and other models in regards to 4 slots of 1066 RAM - motherboards won't accept it as 1066 and drop it to 800. It's not clear from the documentation whether this is a function of the board or the processor chosen - opinions vary here and no one with an older and newer CPU with 4 slots of 1066 has been found to test it.