What do I do? I was told to run water at night because of the tempertures but now I have no hot water.?

I don't know really,but it seems to me a hot water pipe can freeze just like a cold water line and just maybe you have a hot water line frozen.

You do not need to run the hot water line. It is the cold water line that were concerned about and a simple drip would be fine. That is enough to keep the water moving so that the pipe would not freeze.

The water heater tank is full of cold water and it will take about an hour to warm it up again.

The cold-water inlet to your water heater might be frozen.

@MattD: It would be pretty hard to "empty" a water heater without simultaneously filling it with cold water (the vacuum would be huge) unless there is an air leak..

You didn't run hot water all night, did you? If you did, you emptied (and possibly fried) your water heater. Turn the water off for an hour and try again.

You shouldn't run the water all night. You should just let the faucet drip.

Ours is doing the same. It's too cold to shut it off. We didn't run hot water.