vcc-to-ground-hack? I guess it may result in failure of PSU...
I suggest serial first: You have 4-pin linear connector on the boards corner.
That's serial. http://wiki.openwrt.org/toh/asus/wl500gp#serial
Pin 1 (with the square solder pad) is RX0.
For (WL-500gP V2) tts/0 is on the J4 connector:
The header probably is not soldered, so you have to do it. +3.3V and GND are at the ends of the connector.
You can identify them either visually or by multimeter. RX and TX are the two middle pins.
If you have an oscilloscope, you identify it so --- on TX pin during power up there should be some activity --- console output.
If none you can skip to JTAG directly ,because console and pin 9 already not helpful. If you don't have scope then trial and error is ok.
Next you have to make level convertor. Router's rs232 uses 3.3/0V logics while PC uses +12/-12V. It's 1 chip and 5 capacitors.
Look in the datasheet of max3232 at maxim-ic.com for connection. On my experience max232 also works fine despite it's 5V chip.
Finally, you connect router through converter to rs232 of PC, set 115200 as speed and if it is alive you should get console output
which may help to diagnose what is wrong. http://adm5120.narod.ru/max232.htm
Pinout of JTAG I've seen somewhere on the openwrt site. http://adm5120.narod.ru/ejtag-adm5120.htm
There should be probably description of JTAG-LPT connector and what is needed to do, but I don't have experience with this.