Maybe give it another reset? Did you follow the instructions exactly when resetting? The exact technique to use the reset button varies between products and unfortunately some have been known to corrupt the firmware if incorrectly reset, which would give symptoms similar to what you describe.
Check out
this page on Seattle Wireless. They have some useful tips on getting serial and JTAG ports to work which may assist in re-flashing the firmware.
Edit:
Your model appears to use Broadcom hardware. If you manage to get a working serial console I've got a
few tips on getting firmware back on using the Broadcom CFE interface. I guess there isn't any reason why firmware such as
DD-WRT shouldn't work either so it might be worth a try (at your own risk of course).