Brick
you most probably flashed wrong firmware, not dedicated to your hardware. heh? other reason could be loosen heatsink, thats common that when system is unstable [too hot, cooling problems] then kernel wont load due to errors.
[below you can read on your own responsibility]
first try to powering on with serial console active and 1 pressed as kilnakorr suggest (http://forum.wdlxtv.com/viewtopic.php?f=&t=6753). let see what will happen... in my case [my kernel was ok] that's do nothing special, just boots from nand.
if that wont help then you can use yamon to boot new kernel loaded from ram [sucked from tftp]. to get into yamon just after powering on with serial console active press 0 and keep it.
first you need to setup tftp and nfs server to provide required firmware files [in example at 192.168.1.123 host]. then go back to box and setup networking:
setenv ipaddr 192.168.1.100 setenv subnetmask 255.255.255.0 setenv gateway 192.168.1.1 load -b tftp://192.168.1.123/wdtvlive.fff 0x84000000
the hard part is to load rootfs needed for boot, tftp is limitted to ~32MB and thus you need to use nfs. even there are original roots from 1.02.21 that size is below 30MB its compressed romfs and i was unable to load it through tftp.
[at this stage you are on your own as i have not crossed that line!]
load -b tftp://192.168.1.123/wdtvlive.fff 0x84000000 go . root=/dev/nfs nfsroot=192.168.1.123:/wdlxtv/wdtvlive.bin ip=::::::dhcp rdinit=/none console=ttyS0 mem=135MB
use setxenv for other interesting possibilities. and better next time watch what you are playing and what firmware you are loading. wish you success with debricking [as i have ].
Additional resources: http://forum.wdlxtv.com/viewtopic.php?f=3&t=6595 http://wiki.wdlxtv.com/WDTVLiveSerial