Disabling focus on a form

i created a button on a form(SHOW button on Electronic diary) which is supposed to link to another form(Appointment Details) so i can enter details...

My problem is, when the Second form is open, the previous can still be accessed and used(still active) and i want a situation where only one task can be done at a time (this way, you cant add new appointment while showing details..etc).

Please i need help on how to disable the access to the prev form(Electronic Diary,even tho its still open) i have attached a copy of the image of both forms so as to further give you a visual image of my prob. thank you :-)

alternative solutions are also welcome :)

Use a modal dialog.

Set the 'enabled' or 'visible' property on the other dialogs/controls.

Handle changes in the 'focus'.

Thanx you all for all your advice. for all of you who might be experiencing the same problem

i initially used this code, which was the reason for me posting this problem

Code:

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Appointmen_ShowScreen^ showAppointForm = gcnew Appointmen_ShowScreen();
                        showAppointForm->Show();

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then i realised to make the only active form(showAppointForm) the only accessing form out of the two, i used the showDialog method instead.Below is the code

Code:

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Appointmen_ShowScreen^ showAppointForm = gcnew Appointmen_ShowScreen();
                        showAppointForm->ShowDialog();

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THANX!