My arduino mega 1280 works propely, that means, it executes the sketch it currently has in its memory.
Problem is, if i plug it to the computer it says "device not recognized", so I assume the bulit-in ftdi converter is dead. How can i still program the atmega using a "common" ftdi adapter??
By wiring the send and receive TTL serial signal lines from the new ftdi to pins 0 and 1 (or is that 1 and 0, I always get in mixed up
) on the arduino mega shield connector, plus a ground wire from the FTDI adapter to a arduino ground pin, and you should be back in business.
But first you should check to make sure you don't just have a corrupted or missing FTDI USB driver in your PC. Try deleting it and re-installing the FTDI driver and see if that works before going with a new external FTDI serial cable.