Try removing the wireless dongle and going to network (wired) setup. From there, restart the television, plug in the dongle, and select your SSID again and see if that does the trick.
Would you have a dual-band router, by chance?
I have connected the Samsung USB wireless adapter to my LN52B750 TV and it will recognize my home wireless router but it mistakenly thinks the encryption is WPA. The wireless router is WPA2-PSK. How can I change it to recognize the correct encryption method? Thanks Gary