Possible Blown head gasket

2002 Buick Century. Mileage: around 77,000. Engine size, I think is 6 cylinder. I was leaving my driveway the other morning and just as I got to the road, my car shuddered and died. I thought it could have been a possibility that I ran out of gas, so tried that first. Still would not start. Tried replacing the spark plugs, also did not fix the problem. My father in law took a look at it and said there is oil in the radiator which indicates a blown head gasket. Before I pay the money to fix that, I want to be sure that is the problem. Before this morning there was never any indication of any problem. It never overheated, and I had just gotten an oil change about 2 weeks prior. PLEASE HELP! You would not believe the bad luck I have with cars, but this one is still being paid for, so I really need to get it fixed, and dont have the money to take it to a mechanic