Convert text to decimal

Please i'm trying to convert a string to decimal but i can't 
what is the problem please

Dim temperature As Decimal = Convert.ToDecimal(TextBox1.Text)
If temperature > 37.5 Then Label3.Text = "Temperature out of range" ElseIf temperature < 0 Then Label3.Text = "Temperature out of range"
Else While (temperature <= 37.5) If (temperature = 36) Then Label3.Text = "Temperature too low"
ElseIf (temperature = 37.5) Then Label3.Text = "Temperature too hight"
Else Label3.Text = "Good Temperature"
End If
End While
End If