@Arielaaa 

If you look at the RE450 is the LED for the 5GHz turn on or off?

What is the model number of your wireless router?

@Tony 

Hi, 

yes the LED 5Ghz is on. Both of them is on (I mean 2.4 and 5)

when I try to connect the 5 ghz I got the message on iPhone/PC "No internet connection" and it's failed to connect the Extend WiFi .

The model is RE450

@Tony 

my router is of router is Technicolor DGA2232

@Arielaaa 

Go to the wireless settings for the 5GHz, change the authentication to auto, and change the encryption to TKIP/AES. Once that is done, unplug the extender and plug it back in.

@Tony I don't have this option.

i have only - WPA2 PSK, WPA+WPA2 PSK, WPA2, WPA+WPA2

@Arielaaa 

Try both WPA2 PSK, WPA+WPA2 PSK, save, and rebooting the extender.

@Tony 

hey

Now i always success to connect the extender but sometimes the internet working and sometime no.

Mostly there is no internet but my computer/iPhone connect to the WiFi

@Arielaaa 

If you notice no internet from the extender, look at the circle LED light. If it ever turns red, move it closer to the router so the circle LED is always solid blue.

@Tony the circle LED light is blue. The extender connect well to the router. But when you try to connect the extender via iPhone or computer, there is no internet access.

@Arielaaa 

If the 5G turns on, but there is still no internet I would recommend following up with your local support: link