This is a TL-WR741ND v1 but will only accept firmware with a Rosewill vendor byte in the file header. OpenWRT currently does not have the byte by default. DD-WRT has everything we need, so we can use it to bootstrap. (As an alternative, you could try the script made for the RNX-N300RT to add the missing byte to the correct firmware file for this router. At the time of writing, the script method is untested for this model. Please add your experience to this wiki page if you try it.)
Serial Connector Soldering is the only way to recover, be careful! THERE IS NO WAY TO TFTP OVER ETHERNET.