batata004:
Great man, your diagram made it very easy! Now I understood it, the currenct from USB has to pass thgourht 5v pin and if its too much current it may destroy arduino.Thank you! This problem of mine is not "rare", I am amazed that there are no more idiots like me making this same mistake.
The voltage from USB connects to +5V, (via a Schottky diode), then flows back through the regulator to your LED which is connected to Vin. The whole Arduino isn't destroyed at that stage, just the regulator.