Problem with a new Arduino Mega

I just installed my new Mega 2560 and I can't get it working.
Something I noticed is the L led start blinking as soon as I plug the USB cable and keep that way no matter what.
I wanted to try the Blink example but as it uses the 13 pin (which as i said, is already blinking) i just modified to make it use the 12 pin, script compiles (at least that's what IDE says, and at that point L led keeps blinking) but the led connected there never turns in.
There is no activity over TX and RX leds.

Any idea what is going on?

Thank you.

EDIT: In some way I got it working, no idea how tho :roll_eyes: