The link led should light up. Else it could be something wrong with the fiber connection. Ie the fiber connection is loose or the fiber is broken or your area is having maintenance.
You can try one of the following
1. Unplug the fiber and plug in again, make sure that it is tightly connected. If this doesn't solve your problem, then

2. Ask your neighbour whether he is having same issue. It could be the fiber dp box is faulty or your area is having maintenence. If his Internet is ok then most probably the fiber cable connecting to your house is broken, it can be outside or inside your house.

If this is the case, you have to call maxis and ask them to arrange for tm technician to come fix your fiber cable.

Sometimes maxis call center maxpert have no clue what js going on, you have to tell them your problem. Tell maxis that the link led is not light up. That you suspect fiber is broken and ask them to arrange tm to come over.

There is a minimal chance that the Alcatel btu is faulty. I experienced once 2 years back where my Internet would randomly disconnect and the btu leds would randomly blinks.

Tell maxis that you have done all the troubleshooting and you are sure that fiber or btu is faulty cause the link led is off.