M4A78 Pro and Phenom II X2 550 Will not post

I have been searching for days and have seen more relevant information here hence this posting. I have been running an Asus M4A78 Pro motherboard with 2Gb of Gskill DDR2 1066 memory and a HD 4850 video card as well as an AMD X2 4800+ CPU and everything runs great... Until I decided to purchase the cpu in the title above... a Phenom II X2 550. After initial install the system would power on but not post. No beeps, video, etc... fans would spin up, LEDs would come on, HDD's and DVDrw would spin up but nothing else would happen. Before I installed the CPU I set everything to AUTO/ default in bios.

So first thing I did was re-install the old 4800+ CPU clamp down the HS+Fan flip the switch and BOOM everything works as if nothing had gone awry. I go back into bios and attempt to see if there was anything I needed to do as far as clock/ multiplier settings but everything was in auto so it should have been ok. Thinking that the new CPU may have been too much with all the other hardware for the Corsair 650 or so watt PS I disconnected everything powered up with the 4800+ checked it out then shut her down again to install the X2 550. Again with nothing but 1 stick of memory in Dimm1 and the ps2 kb attached the system fans and such would whirl into life but no post, no beeps, no video. I also removed the add in video card and tried to use the onboard... still nothing.

I then removed everything from the case and set her up on my desktop and reworked the original config. She booted right up no glitches. I checked the BIOs revision and even though the version I had supported the X2 500 there was a newer version out so I re-flashed my bios. I checked the BIOs settings to make certain everything was in auto shut the system down and then removed everything but 1 stick of memory and the ps2 keyboard. I then installed the Phenom II cpu and the no boot issue was still there. At this point I started to shut down the system and move the single stick of memory from slot to slot to test to see if it was the memory. The issue remained each time.

At this point I figured that the CPU must have been faulty so I returned it for replacement listing all the above. The new CPU came in and I went through all the above listed steps once again minus the bios flash. Asus lists this CPU as being supported; however, it seems that a lot of ppl with this particular mobo are having difficulty installing Phenom II Cpu's. It seems there are a few people that have been able to get this motherboard to work with the X2 550 but they've not posted their findings/ settings. Well at least I've been unable to find them. I don't think that 2 retail CPU's are going to be bad Back to back but that is a possibility.

Any suggestions would be greatly appreciated. Oh and I've not set ACC or anything atm to try to unlock the other cores at this point. Once I get a stable system THEN I might try it one day in the future but currently my only goal is to get it to BOOT and then maybe just maybe I'll start tinkering with it.