The arm normally was on around 125 degrees now it is not registering anything. It is below all the numbers. And I can't find where you put water in the engine to check the water level
The temperature arm is not pointing on anything on 2005 Chevrolet Cavalier
Check the overflow bottle for levels, add water through overflow bottle. If the overflow bottle is empty, wait for the vehicle to cool down before opening the radiator. Make sure there are no air pockets, by raiseing the front of the car or use an evacuator (airlift tool). If levels are good and there are no vacuum leaks, check ECT sending unit for open circuit
Are you getting any heat out of the vents? You need fluid to to get the temp sensor to register on the gauge. Like ccsmog said make sure the vehicle has cooled down before you open the radiator but you can still check around the entire cooling system looking for leaks. The plastic tanks on that radiator are common, so are the hoses near the clamps. Be thorough! If the coolant's gone it went someplace.. Good luck.