You need to check for 120v at each component in the circuit before anyone of us can help, otherwise everyone responding is just guessing.
You said there is power going through the breaker, great. Now check to see if there is power through the switch in the kitchen. If so, move down the line, is there power going through the outside switch at the WH? If so, check if there is power going through the heating element.
After you have checked everything let us know what you find out. We'll be able to help a lot better after everything is checked out.
I had a similar problem, checked everything through the complete circuit and found the outside switch was not working. I replaced the switch and we then had hot water using 120v.