Expected behavior of 555 timer in monostable mode
Without the switch pressed, the TR input is open, hence undefined. With an undefined input, you can't expect any specific behaviour. 

Maybe you intended R1 to be a pull-up? As drawn, it has no function.

What voltage do you expect on pin 6 when you apply power? As drawn, it is undefined. A diode could be added to discharge C1 to the power rail.

And as HandyHowie remarks, the LED needs a current-limiting resistor.