If there no power in the car when I put the key
How do I no exactly what's wrong with my car if my
power just stopped after I get out the car go in the
house for like 2/3 hours an come back out car has
no power whatsoever
Start by checking the voltage on the battery before looking at other issues. Use your multimeter on the connections under the hood in the passenger side of the engine bay. You should be reading over 12V. If not, it's time to swap it out. The battery is in the trunk under the trunk panel on the right and or passenger side of the vehicle.
Agreed, it sounds like you have a weak battery. Check the voltage.