We just had a new gas water heater because the previous one was not heating the water. Well after a whole 12 hours we noticed the water is still not hot. We have already adjusted the temperature knob on the heater and still nothing! Any suggestions?

Well apparently the original problem was not the water heater.
Who installed the new water heater? Water heaters either work or they don't work. Water heaters are most often replaced because they leak, not because they don't work.
Describe the problem, do you not have any hot water? Are there certain faucets that the water is just not hot enough?

Tell us about it.

it was intalled by homedepot. There is no hot water at all in any part of the house

Does the burner come on?
Have you had any hot water since it was installed?

I agree with Harold, you should call HD back out, they warranty their installation

Have you checked the breakers or fuse box?

it is a gas heater, I didn't even think to check the breakers. I have not had hot water since its been intalled, but I didn't have hot water before the new heather. That is why I am thinking it was not the heater. Could it be the plumbing?

Unless the water heater has some kind of powered vent motor no breakers should be involved.

Is it that the water is only warm or do you not have any hot water?
Does the burner come on if you open a hot water valve for a period of time?
If you only have warm water, open the water heater drain valve very briefly. Is the water that comes out hot, cold or warm?

OK I just opened the water valve to the heater and it is luke warm. What does this mean?

See below


Unless the water heater has some kind of powered vent motor no breakers should be involved.

Is it that the water is only warm or do you not have any hot water?
Does the burner come on if you open a hot water valve for a period of time?
If you only have warm water, open the water heater drain valve very briefly. Is the water that comes out hot, cold or warm?

Means water in heater is not getting up to temperature and problem is not a plumbing problem such as hot and cold are getting mixed somewhere such as a defective washing machine mixing valve.
Suggest calling installer, water heater may be defective.

You don't have any kind of recirculation line do you?