Q: Saab wont start, or crank, check engine light, "coolant sensor" is on

Starting with the coolant sensor. While the coolant sensor may be an issue, rarely if ever will a failed coolant sensor prevent the engine from cranking. It usually will just effect engine performance and economy. If the engine shut down the last time it ran, it’s possible there are other issues that caused it. If the engine was overheated, there may be internal damage to the engine, possibly causing it to seize. A no crank / no start issue can be due to a damaged engine or even a failed starter. If the starter is easily accessed either underhood or under the car, grab a small hammer and a friend. While one of you holds the ignition in the Crank/Start position, have the other lightly tap the starter with the hammer. If the starter has a "dead spot", sometimes batter power from cranking and the light taps from the hammer will move the starter internals enough to start the vehicle. If that does not work and you are interested in finding the exact cause of the no start before deciding to get rid of the vehicle, have a certified technician inspect the vehicle to see if it is worth repairing.