To Check if a Form is open in C# and VB.NET you can use the snippet below.

Sample C#

public static bool FormIsOpen(FormCollection application, Type formType)
{
	//usage sample: FormIsOpen(Application.OpenForms,typeof(Form2)
	return Application.OpenForms.Cast<Form>().Any(openForm => openForm.GetType() == formType);
}

Sample VB.NET

Public Shared Function FormIsOpen(application__1 As FormCollection, formType As Type) As Boolean
	'usage sample: FormIsOpen(Application.OpenForms,GetType(Form2)
	Return Application.OpenForms.Cast(Of Form)().Any(Function(openForm) openForm.[GetType]() = formType)
End Function