I would do the following, download the latest FW build for your region, unpack the .bin file.
http://suporte.dlink.com.br/suporte/produto_detalhes.php?fa=RElS&eq=NjM2TA==Using IE or FF with add-ons and any PC 3rd party security programs disabled temporarily.
Turn off ALL other devices and connect up 1 wired LAN pc to the router. Disconnect the ISP modem from the router. Just you, PC and router.
Factory reset the router from the Tools/System menu.
Send the .bin FW file from the Tools/Firmware and let it process and reboot.
After it reboots, do one more factory reset, plug in ISP modem cable and then set up the router from scratch.
Setup SSID and PW, try single mode G, WPA2 and TPIK only and test your WiFi devices.
Let us know the results...