You did unplug the PSU wall cable and held start button before that battery exercise?
Hanging boot meens one or more components arent responding (less its corrupt bios). GPU, RAM, HDD's, CPU. Even in some cases you still need a ps2 keyboard connected (older comps).
Anyways take out all the ram, and if you have a spare GPU try that with one RAM stick at the time. If you have more than one HDD, also try them one at the time.