I had that happen last fall with my 07 Impala. Things showed power , battery OK, but many various things won't work: engine wouldn't turn over, power windows
wouldn't work, trunk release no working, dash display comes on delayed , key won't come out, radio not working , door locks not working, and some other things.
It turned out to be the BCM circuit. I ordered a used one off EBay from the same year and model of car and same part #. Installed, then everything worked
again but radio was locked and engine service light was on, code saying to re-align timing sensor( I think cam but not sure). Anyway, at least I could drive
40 miles to closest GM dealer to reprogram the BCM for the car and do the alignment for the sensor, then all was good. The used BCM was $65,
dealer re-setting things was $50. This may not be your problem, but worth considering if
no fault is found with the power/battery system.