iBook - flashing green charge light?

I just bought a iBook G3/900 today and the PMU needs to be reset but I dont know how, the battery is completly dead now and when I plug in the charger it should be an amber circle but its pulsating green. I'm sorta confused I hope its just pulsating because its so dead and I cant turn it on now but Im guessing its because theres something wrong.

Edit**

I've tried to pmu reset with no results I tried to do cmd-option-pwr and nothing, I took the battery out and still pulsated and resfused to turn on