Startet with an Arduino Uno board and have programmed it lots of times without any problems. Now i just bourght some Arduino Nano and first time connecting it, the "L" led flashes, and programming went well.
But if i tried a second time the LED didn't flash and i was unable to program it.
I have read about the bootloader, but don't have the hardware to burn it.
Is it just a rookie mistake?
(Arduino Nano board with FTDI chip. FTDI driver installed correctly)
/Rasmus
In the IDE preferences check the option show verbose output on upload.
Upload a sketch, and when you click the upload button in the IDE, also press the reset button of the Nano. Release the reset button when the IDE changes from Compiling to Uploading.
I have tried that. Doesn't work 
Using Port : /dev/cu.usbserial-A600KRM4
Using Programmer : arduino
Overriding Baud Rate : 57600
avrdude: Send: 0 [30] [20]
avrdude: Send: 0 [30] [20]
avrdude: Send: 0 [30] [20]
avrdude: ser_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding
avrdude done. Thank you.
Hmmm, well you could try burning the bootloader fresh on the Nano. Since you have an Uno, you can use it as a programmer. Load the example ArduinoISP sketch onto the Uno. Then install a 10uF or larger capacitor on the Uno between Reset and GND, with the striped or neg lead on GND. That will disable auto reset.
Connections:
Uno Nano
GND GND
5V VCC or 5V
10 RST
11 11
12 12
13 13
Connect the Uno to the computer with the USB cable. The USB port on the Nano should be disconnected. In the IDE choose the Uno port, Uno board, and choose "Arduino as ISP" as Programmer. Choose Burn Bootloader. If you get the Done burning bootloader message, it worked. Since it has the Uno bootloader on it now, you can choose Uno from the board menu when you program it.
If it worked, disconnect wiring and connect the Nano to the USB wire, and upload a sketch such as the blink sketch.
Thanks dmjlambert
I installed the latest Arduino release and then it worked with your reset trick!