Unifi No Internet Access or WAN light turns Orange

Last two day I've encountered connection issue with my Unifi, there was a yellow triangle with exclamation mark over network‎ appears at the bottom right corner of screen. By clicking it, it shows no internet access and undefinable network in control panel. Unifi modem, HUAWEI HG655a Home Gateway and wireless router-RG TMRND Gen1.0 wireless-N Residential Gateway are function properly. All lights on either solid green or blinking, except the WAN light on wireless router turns to solid amber/orange. Wireless signal is there, but no INTERNET ACCESS as well.

So I call the services centre, the Rep just ask me to check the light one by one, and said there would be some connection problem in my area or the router problem, they can't define the problem on the spot. So they would arrange a technician to come over, not sure when, and give me a case number.

After this I spent another 2-3 hours to self-check the cable, the network setting and also the computer settings that might cause internet connection failure. All devices ok, my friends at the same area can online, but slow (it  always happens).

I think it could be my setting problem, so I call the service centre again, and this time there was another Rep answered the call. She said they have record in their system and will arrange the appointment as soon as possible, she also want to end the call quickly, didn't spend time to understand my problem. I told her I have reset my router to factory defaults and request her to guide me through the setting. So she did, but I still can't connect to internet, another day of no internet access for me.

The next day I received a call from the technician to make a appointment (the first time they respond fast), but I can't make it as no people at home during weekdays. So make an appointment on weekend =(

Today, I spend one hour surfing  internet and look for similar connection issue, I go back and try. Connection problem solved. Here is what have I done. Unifi No Internet Access/No Connection[SOLVED]