Van engine shuts down after about 2 miles of driving

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I have a 1994 GMC Vandura 1500 and the radiator recently froze. It was also low on oil. We managed to thaw the radiator, put in antifreeze, filled the oil. I was able to drive it the next day, all day, and then, the following day we were able to drive it for about 30 miles or so in town. On the way back home, it shut down again. I had the battery tested and replaced. It started fine and I drove it this morning to take my daughter to school. I got back home, it sat for about 4 hours and I had to go back into town. About 2 miles down he road, it shut down again. I'm not sure if we damaged the engine at all during the freeze of the radiator/low oil. It sounds like crap, but I assumed that was due to the muffler being damaged during a tow. Now, I am thinking it may be due to the engine. It does sound like knocking but like I said, I thought it was the muffler, as it did not make any odd noises until after the tow truck driver "dropped" the back of the van on my driveway when he was unloading it from the truck. It was on a roll-back truck and when he was unloading it, it slipped and the rear end of the van hit the pavement. I assumed that was what was causing the noise, as the muffler pipe was then cracked. Any ideas on what could be going on? Could the muffler pipe being cracked cause something to shut down? Could we have blown the engine? There are no check engine lights coming on or any other lights other than my airbag/abs lights which have been on for a long time.