1998 Saturn SW2 Oil

I was driving and hard a quick grinding noise come from the engine. The service engine light came on. I drove home for about 2 miles. The car drove fine all the way. When I got home I opened the hood and looked. Engine was not hot or over heating. I decided to check the oil. I took the oil stick out but did not see much oil on it at all. I wiped it off and rechecked it. It was bone dry. I never saw the engine oil light ever come on, either. I started to add some oil, wondering why it was so empty in first place. I got abot a half quart in the engine and it filled up to the top where you add the oil. I waited a miute to see if it would go down (because it is cold up here today) but it never went down. So I went back into the car to start the engine to see if this would help it too go down. It did not. But now the oil had a little discoloration in it like it mixed with the antifreeze(not sure, about head gasket). The car still starts up fine and runs smooth. But the dip stick still does not register any oil. I checked to make sure it was all the way in and it is. Do not know what is wrong?