I just bought and installed a new presser tank but there's no water going in to the tank
Need help

Don't you mean "pressure tank"

I just bought and installed a new presser tank but there's no water going in to the tank
Need help

I'm guessing someone forgot to turn the water back on. Because it HAD to be turned off to replace it.

I'm not sure what you mean by "no water going into the tank". Do you mean that you are not getting water from faucets at all, or that it is your impression that the tank has very little water in it? If it is the latter, then that is not unusual for a new bladder pressure tank. It will resolve itself in a few weeks as the air under the bladder is absorbed by the water and opens that area to be filled by water only.