2015 Chevy (Holden) SS, 1989 Milano (Shankle Sport), 1991 164S
If it won't crank when hot but will when cold, sounds just like the problem I had with a GTV6. Turns out the firewall ground wire was dirty and loose. Had aux power for radio, etc, but no crank when hot. Once cleaned and tightened, it was never a problem. I would start at the battery, charge it since it also could be a low battery, clean the connections and retighten, then clean and tighten all the grounds in the engine bay you can find. also, check the connectors for the starter power cable.