Why don't I have power?

Make sure the batt terminals are clean and tight , there may be a relay , check fuses , mega fuses and fusible links , something else may have gone bad by pure coincidence

Fuselinks, ignition switch, clutch or neutral safety switch or even a bad starter especially if it is a remanufactured unit.

I'm guessing you replaced the starter yourself and didn't use a memory saver to maintain power in the vehicle when you disconnected the battery cable from the solenoid. when you reattached it, you likely blew at least one fuse. Or the damager might be in the computer. Check fuses and if they're OK, have a mechanic find the problem; might be kind of expensive.

1980 did need a memory saver tool. What computer it had was hard programed right in the chip.

Didn’t need. Spell check didn’t get it right.