Some firmwares failed on a ASUS WL500-GX

I have a problem with a ASUS WL500-GX. I used it for two months with koppel firmware ver. 1.71, with an Icon 225 3G modem.
Two days ago I had found it blocked (LEDs ok, but no ping). I restarted it ( unplug and plug power cable) but the same problem. I try to put again the firmware, it enter in rescue mode (respond to ping on 192.168.1.1, accept conection tftp, also with Asus Firmware Restauration Utility), but after uploading the firmware no booting up. Power LED and LAN 1 LED on, rest of them off.
Strange is that I managed to come alive the router with no problem, using openwret, dd-wrt, and versions 1.60 and 1.61 for Koppel.

Any ideea for that problem?!?

Thanks