I had R2 working last night for the first time, but the batteries were at 15% so I charged them, and now R2 goes through the initial test, goes forward a couple CMs, turns his head back and forth, then his light fast flashes purple, what the guide says is Startup Stage 3, and never gets past that.

If I press any of the buttons, I hear three clicks from inside, and R2 hangs. The light goes solid purple and pressing any of the buttons do nothing. I have to flip the switch and if I turn him on again, it just does the about routine again.

He was working great last night, not sure what happened.
Since he was working, I assume the cables are plugged in right and the right way around.

But if you want me to open him up and check I will.

Ok well the issue was one of his dome plugs did indeed come loose. And when I pulled his head off, one of the far and deep down plugs came out :-\
My fat fingers couldn't get it back, so my 17 year old daughter with long slender fingers was able to plug that one in, so FYI, if your R2 is never getting past startup stage 3, one of the dome plugs probably came loose.

Now his arms don't retract properly, but that's probably when I was dicking around trying to plug in the errant plug, I bumped the gear arms and now they just refuse to cleanly go in and back. But that's on me. I just hold them in place, hit the button and they sit. But oh well I'll never really use that feature anyways and may just Krazy Glue them in place.

And on a side note...He's beautiful <3 <3 <3