Can you provide a link to the Nano's you have?
Are these official Arduino Nano's or clones?
Which bootloader are you flashing onto them?
Start with the ASCIItable example or something similar to that.
Definitely the change of the FTDI driver back to 126.96.36.199 solved my Problem !!!!My Arduino Nano is a SainSmart V3.
For win8Control Panel -> Devices and Printers -> Click on the FT232R USB UART -> Select Hardware from the top -> Properties -> Change Settings -> Select Driver from the top -> Update Driver -> Browse my computer for driver software -> Let me pick from list... -> Select the USB Serial Converter Version:188.8.131.52 [10.4.2012] -> Done Trick: Do not select the new Version:184.108.40.206 [18.1.2013]The same solution may be used for the PL2303 chip driver. Always, select the old version of all drivers .