Using the Option Inspector works for me. Alternatively, you could use:

SetOptions[$FrontEndSession, 
 CommonDefaultFormatTypes -> {"Input" -> TraditionalForm}]

Then, new notebooks will use TraditionalForm.

Using the Option Inspector works for me. Alternatively, you could use:

SetOptions[$FrontEndSession, 
 CommonDefaultFormatTypes -> {"Input" -> TraditionalForm}]

Then, new notebooks will use TraditionalForm.

As far as I know, Mathematica never converted input cells to TraditionalForm upon using Shift-Enter. If you do want to have the cell converted to TraditionalForm automatically after using Shift-Enter, you can do this with a stylesheet. For example, the following cell expression in a stylesheet should do what you want :

Cell[StyleData["Input"],
    CellEpilog :> With[{obj = EvaluationCell[]},
        SelectionMove[EvaluationCell[], All, CellContents];
        FrontEndTokenExecute["SelectionConvert", "TraditionalForm"]
    ]
]

Using the Option Inspector works for me. Alternatively, you could use:

SetOptions[$FrontEndSession, CommonDefaultFormatTypes -> {"Input" -> TraditionalForm}]

Then, new notebooks will use TraditionalForm.

Using the Option Inspector works for me. Alternatively, you could use:

SetOptions[$FrontEndSession, 
 CommonDefaultFormatTypes -> {"Input" -> TraditionalForm}]

Then, new notebooks will use TraditionalForm.