Without examining your return, it's impossible to say exactly what caused your refund to decrease ( or not receive anything).
If your refund is wildly off, it's possible you simply mistyped a dollar amount somewhere. An extra digit here, a missing number there, even something as seemingly insignificant as a misplaced decimal point can have an eye-popping effect on your TurboTax refund.
The tax laws changing year to year will determine the amount of taxes that need to be paid as well.