Being able to input text depending on drop down list.

[SDMElektro]

Now here's my problem.

I created a drop down list in one cell. It basicly has only 2 options. Yes or no.
I want to lock the workbook for users, so they can't alter cells but the ones I want them to.
If that particulate cell, lets name it D1 has value "No" I don't want users to be able to change the value in E1.
But. If the value (from the drop down list) in D1 contains "Yes", I want the end user to type in E1 whatever they want.
How do I do this?
I know I need Data Validation. I just can't figure out the formula.
The real point is that I found how to.
But when the value of E1 is entered and the value of D1 changes, E1 stays unchanged.
Is there a solution to this? Without macros?
Please help.

[6StringJazzer]

But when the value of E1 is entered and the value of D1 changes, E1 stays unchanged.
Is there a solution to this? Without macros?

If the user enters "No" into D1, you can prevent further changes into E1 with data validation. Custom rule:

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BUT once a user enters a value into a cell, there is no way to change it without macros.