I have a 1992 Mitsubishi 3000 GT SL. It was running ok, but in May, 2015 I put the car in the garage and haven't driven it since. It won't start...did I ruin my car?

Sounds like could be bad gas. If it's dohc it requires premium high octane fuel to run properly. Old gas gives these cars fits. I would empty out all the gas, add new high quality fuel, loosen fuel line at fuel rail place catch pan under line and use fuel pump jumper behind the battery to energize the fuel pump and allow to pump till new gas comes out, re attach fuel line, replace the fuel filter, remove clean and or replace spark plugs, also check air filter because small rodents tend to nest there. This should get you back running fairly cheaply.

Good ol popcorn gas oil separates when it's not in use. And can clog up fuel lines fuel filter. I would check there first. When I replaced my fuel filter it smelled like Orval rednbacker popcorn lol and when I blew it out it was all yellow and dark looking. I'm using a aftermarket cleanable filter from JMD aluminum now.