I start experimenting with an Arduino Pro-Mini. So I connected a FTDI to my PC and upload the blink sketch, via PORT 3 (I have confirmed that this is the corresponding PORT).
The think is that the on-board LED behaves randomly. For example, I upload the default 1000 msec delay, and I can see the LED blinking, with a period of 2 secs. When I change that value, making it smaller or bigger, the led is flickering and the light is very dim. Sometimes, if I disconnect the arduino board and reconnect it, the LED will work (with the "new" delay value), but after a while it "crashes" again and starts behaving strangely.
Any ideas on what causes this?