See if this is what you want:
Sub TestNumber()
Dim myNumber As String
myNumber = InputBox("Enter your number below:", "Numbers only please.")
If myNumber <> "" Then
If IsNumeric(myNumber) Then
MsgBox "Click OK to continue the macro.", 64, "Valid number value was entered. Thank you."
Else
MsgBox "You did not enter a number value, try again.", 16, "Get with the program!!"
End If
End If
End Sub