Similar steps can be used under Linux, I have no idea how to Windows anymore. This will probably work for similar Buffalo WZR routers, though your milage may vary. These directions flash the router back to stock Buffalo branded DDWRT.
When these routers brick they tend to go into a kind of reboot mode. At the begining of the reboot, the TFTP server is available for a brief period of time, then all of the lights flash and the unit reboots. We're exploiting the short period of time where the router is in TFTP mode at the start of the reboot. You can try to do a put via TFTP at the begining of this cycle, even if your router has been plugged in for awhile.