Did he relight the pilot, and is the switch set to run?
Check and see if the temperature setting was changed, if it's really an electric check and make sure it's plugged in and that the fuse/breaker hasn't tripped. Heck, even gas water heaters use a tiny bit of electricity so you might look in the breaker box to see if it has one labeled water heater anyway.
Easy things to check yourself, and sometimes it's the simple things that are most overlooked.
Many years ago I spent the better part of an hour watching my hubby cussing at the furnace trying to get it to ignite before I mentioned that it might work better if he opened the valve to the fuel oil tank. The guy had closed it the day before when he filled it up. Even though the house was soon toasty he saved one could shoulder just for me :D

Hi,
The repairman came and fix the leaked pipe only, he's never touched the water heater. Is the Water heater automatic shut off and we need to relight?
Thanks alot
(PS: I'm a single mom and bought the house 2 years ago, don't know much about that)

Do you mean no flow of hot water, or the water isn't hot? In the first case, the h/w inlet valve may still be turned off. In the second case, he may have shut down the hwh and forgotten to turn it back on. One way to check is to put your hand on the outlet pipe and see if it is warm.

The leaked pipe is outside of the house and he came to fix the leak and then he left. The Water Heater is inside and upstair, so he did not do anything to Water Heater. When I open the hot side, water coming out very strong but very cold.
Thanks