New CPU won't let me post

[Braedley]

A GPU failure in my secondary machine has basically necessitated a near complete replacement of the internals of said machine. In order to do that, I purchased a new CPU so that my current CPU can go in a spare mobo. So now for the details:
Current mobo is an Asus M3N72-D (socket AM2+, nForce 750 SLI chipset)
Current CPU is AMD Athlon 64 4600+ socket AM2
New CPU is AMD Phenom II X2 550 socket AM3

I've already updated the bios, checked RAM combinations, disconnected the GPU, etc etc.

The pros I've talked to agree that it should just work. Other than a bad CPU, does anyone have any ideas?

Also, I should point out that other than the PSU and CPU, the system is exactly the same as what I've been running for the past few months, and since Dec., I've swapped the GPU and RAM.

[General Zod]

Uhm. . . .looks like the CPU is the culprit here. I hope you have the receipt.

Socket AM3 breaks compatibility with AM2/AM2+ processors due to a subtle change in key placement. The AM3 socket has 941 pin contacts[1] while current AM3 processors have only 938 pins. Tom's Hardware removed the two obstructing key pins from an AM2+ Phenom processor in order to fit it into an AM3 socket. The processor did not work in the AM3 socket, but still worked in an AM2+ socket, suggesting that compatibility issues run deeper than merely the key pins.[4]

[Braedley]

You have that backwards there Zod. AM2 boards are forward compatible with AM3 chips. AM3 boards are not backwards compatible with AM2 chips. I have an AM2+ board, AM3 chip. All should be good in the world.

[tezunegari]

What exactly is your problem?
Am I right to assume (without making an ass out of you and me, lame joke I know)
that you have problems with booting your repaired computer (Power On Self Test)?
How far do you get with the boot process?

Did you try to reset your BIOS settings to factory default?

AM3 boards are not backwards compatible with AM2 chips

I think that AM3 boards are incompatible because they require the CPU to have a DDR3 controller. AM3 CPUs have both a DDR2 and a DDR3 controller but AM2/AM2+ CPUs only have the DDR2. Could be wrong though.

[Marcus Aurelius]

You have that backwards there Zod. AM2 boards are forward compatible with AM3 chips. AM3 boards are not backwards compatible with AM2 chips. I have an AM2+ board, AM3 chip. All should be good in the world.

A puzzling problem, indeed. My guess is that either the CPU or the PSU is simply DOA. You can of course test the PSU with the older CPU, but unless you have another AM2+/AM3 MB, there is no way to reliably test the CPU. The Phenom II X2 550 is not very demanding on the PSU (TDP is only 80 W), so it should work if the PSU is not completely broken. I suppose the PSU is a proper ATX12V 2.x with dual 12V rails? (Which is more important than the actual wattage)

[Braedley]

The PSU is fine as far as I can tell because the first two posts were made using that and my old CPU. I do have another AM2 board, but it's fairly unreliable in the boot dept. already (but once it is booted, it works fine, which is why I don't mind using it for a secondary machine). It's also over 3 years old, and I might not be able to get a bios update for it, so putting the new CPU into that is out of the question.

[Fingolfin_Noldor]

Have you checked that even after updating, the motherboard would support the processor in question?

[Braedley]

Yes. The generalized model name (ie Phenom II X2 550) is listed in Asus' supported CPUs for this board. The only difference is that OPN is slightly different from my CPU, but I'm chalking that up to the fact that I have a Black Edition, not OEM or retail.

[Fingolfin_Noldor]

Yes. The generalized model name (ie Phenom II X2 550) is listed in Asus' supported CPUs for this board. The only difference is that OPN is slightly different from my CPU, but I'm chalking that up to the fact that I have a Black Edition, not OEM or retail.

Try the chip on someone else's board and see what happens.

[Marcus Aurelius]

Have you checked that even after updating, the motherboard would support the processor in question?

It may not even be required. Most AM2+ boards which support Phenom will also post with Phenom II processors, even if the BIOS doesn't recognize the processor correctly. Power problems are of course possible, but most Phenom II's draw less power than their predecessors.

[Braedley]

Considering that my Athlon is working fine with the new power supply, I highly doubt it's a power issue. So I guess the consensus is bad chip. I'll try Asus tech support tomorrow, but if they come up with the same things, I'll call the place I bought it from and see about a replacement.