You get the CPU beepcode when you boot it up? Did you try reseating the processor?, did you make sure that all of the mobo power is plugged in, especially the 4 pin(sounds stupid... but I've done it before, it was hiding under the HS and the build was for a friend of mine, so I just assumed that is was plugged in. It wasn't).
whenever a build doesn't start for me, I try booting with just the essentials, so I take out all but one stick of ram, etc, and then see if I cant get it at least to post.
If you still get the error, try taking out the CPU, see if it still gives you the same error. If at all possible, dig up another AM2 CPU, and see if it does the same thing.
DOA CPU's are actually pretty rare, so I would guess that something else is the problem first. To me it seems much more likely that it would be a mobo issue, but I guess we'll see.