Why won't my cadilac catera 98 crank?

Just to be accurate...it wont CRANK or it wont START? Two different things, that most people dont know the difference. If it wont crank, check the battery. Check for power to the starter and lightly tap the starter to see if its stuck. Check all fuses regarding the ignition and starter. There arent too many reason why a car wouldnt crank, so it shouldnt be hard.

The thermostat opens & closes to keep the water at a certain temperature flowing through the engine. It has nothing to do with starting the car. By cranking do you mean the starter isn't turning over the engine?? Do you hear a clicking sound from the starter??