Below is an image of my N416. I have labeled TX/RX as the opposite of what my FTDI USB to Serial is labeled. (I have found that various adapters label these opposite, so you might have to swap them).
On Windows, look in Device Manager->Ports to determine the COM port. Use a terminal program like Putty, Teraterm, or Hyperterminal. Set the COM port to 115200,N,1,8.
On Linux, the link
https://stackoverflow.com/questions/...u-10-10-maveri provides adequate instructions.
I usually connect to the serial port first, then try to either turn the N416 on (if it is off) or click the reset button (if it is on). If your bootloader is intact, you will see initialization messages. You must hit a key during the initialization to prevent u-boot from trying to load the kernel. From here, you have several options to rebuild the flash.