No power at the key or at the batt. - 1987 Mazda B-Series

Charge the battery, take it to be checked at a parts store Advance auto parts or Auto Zone, When you say no power at the battery that tells me that the battery is dead, if that's not what you meant check the ground wire and battery terminals, clean and reattache terminals to confirmed good battery. If still no power to key see if you have brake lights cigarette lighter etc. accessorie that don't require the key to be turned on, if you get power to these things and still no power to starter the solenoid for the starter could be faulty, I would need more info to diagnose this problem.