Try adding the following lines after all your defs.
if __name__=='__main__':
start()
Also, everytime you call a function it needs to be followed by parenthesis, example:
sign = Button(rootE, text="register", command=Signup)
login = Button(rootE, text="log in", command=Login)
Should be:
sign = Button(rootE, text="register", command=Signup())
login = Button(rootE, text="log in", command=Login())
solved code is ignoring def start?