Pin 13 led has a resistor. I hope you're joking about not getting it to blink.
Feed a led low enough V and you don't need a resistor but at 5V the lifetime is amazingly short.
Back in the 90's I saw a 555 circuit that ran red leds on very short 9V pulses yet allowed a lifetime of minutes.... it said.... I never tried. The purpose of that one was to make very bright pulses for a fake laser.
if you actually are lucky enough to find a datasheet specific to a generic led, grumpy mike has a bit about it on his site. Boiled down, you can plop some high current through a led for a specific max time and max rate and not kill it.
Thats very handy when your multiplexing as it can help you compensate for off time dimness from an array