Hi,
I replaced the elements, but it wouldn't heat. The next morning I had a little warm water and the heater was making noise like it was heating, but I could only get cold water. All wiring seems to be correct. Could the main power source have a short, since it seems to be heating intermittently? Thanks.

How old is your water heater? If it is 10 or more years old, you may have a dip tube problem (although I guess this could happen at any time).

This tube puts the cold water at the bottom of the tank away from the hot-water outlet. If this tube has disintegrated, you'll be immediately mixing the hot water in your tank with the fresh, cold water from the inlet.

Here is a good link with lots of interesting info about water heaters.

Good luck,
WallyH