97 civic dx won't turn over or start. click from ecu. all lights, air, etc. function

[marewrath]

this car has usually, in the few years ive had it, had to crank a bit or 'struggle' to start. it was stolen a couple of months ago for a night or two, and ever since then has seemed to start exxactly on the third crank/ turn of the key, and pretty much every time, though the cranks have been sounding consistently weaker. i drove it back and forthe somewhere today about 6 miles/16 minutes each way, and then about two hours afteri tried to start it, to go somewhere else and it won't crank/turn over at all. the only thing i hear is a single click from the ECU area, an dall the dash lights go on ,the air works, etc. i had the battery checked and allegedly its good (whether the connections are, i guess i dont know, they are definitely rusty). i ve checked a few of random fuses, visually--theyre such a pain and it didnt seem like they were the issue to me-- and believe theyre fine.
this probabl isnt related, but a few months ago my headlights stopped working on low beam. i replaced them, before i realized one of them at least works on high beam, so its not the bulbs.

any thoughts on what this is, what i can look at/try, etc?? im desperate!

 

[XpL0d3r]

When it was stolen, was the ignition popped? Wondering if you have an issue with that or even the starter.

Is the CEL lit?

 

[marewrath]

yes, but rhe check engine light has always been lit--it gives a 420 code, which is cadallic converte under efficiency, but pretty much the entire exhaust system has been replaced since that code arose (after it fell off) and the light remains. are you thinking ecu?