iamnotaplant
Most mobos do not have "post messages" they have only beeps that represent post errors. You also do not have to remove the battery and move the CMOS reset jumper, one or the other will suffice. I also don't know what you mean by "everything is unplugged" as you only have to unplug the 115v power cable from the psu.
RyanSengara
My first guess it that you knocked something loose when you replaced the hd (assuming that you replaced the cpu and vid card earlier and had it working). Check all of your cable connections, reseat cards and ram, find any dropped screws, etc.. If you replaced all of the components at the same time, repost as it may be a different problem.