Pontiac Sunbird

I own the same vehicle, and have quite a bit of experience with the 2.0L engines. If the car doesn't start and worked fine before then 9 chances out of ten your coolant wasn't mixed properly and frozen. Check under the radiator cap and see if it's liquid or a gel; Also try squeezing the top rad hose to see if it's firm or not. The water pump is located on the timing belt on this engine, and will not turn if it is frozen in the block. This means the belt is probably stripping on the crankshaft pulley, and will need to be replaced - the timing will also need to be reset.

This is not an interference engine (meaning the pistons will not hit the valves if turned over) however you will need to get the vehicle towed to a warm garage overnight to let thaw, and check for any interment cracks in the radiator, heater core (check for coolant on the carper inside the vehicle), cylinder head or block. often times when coolant freezes in the block it can split some smaller coolant passages in the engine. A pressure test should verify this. If no problems are found, just replace the coolant with the proper mix along with the timing belt and you should be fine.

I hope this helps! Any other questions, just let me know.

Also, here is a diagram of the timing belt and related components to give you a better idea. The bottom pulley is the crankshaft pulley.The water pump is attached to the engine and not labeled.