Kiril,
Without seeing the entire ethernet and gateway settings, it would be hard to tell, but if your routers private side IP is the 192.168.1.255 and that is what you set the tenor to for the default gateway, that should work. Make sure you put a PC on the same network (192.168.1.x) and see if you can ping the router as well. Also, make sure you are pinging the private IP, not the public as the ISP may not allow a return ping from the source.
If you need further help, you can contact me at mike_voip@hotmail.com