DX3301-T0 problems

Hey,

I live in a shared home. For the first 2 days after this router was installed, the internet worked perfectly.

Then it stopped working. When I try to use it, this happens:

But the ISP router is working and supplying internet. Everything is correctly plugged in and switched on. We have done the off/on, restart thing many times.

The wifi internet in this home does not work for the other people who live here, either. Except, someone moved in after that 2 days and he said he uses it on his smart tv but it doesn't work on his phone..

This problem has literally been here for months. I gave up and started paying for my own mobile internet access, but I really shouldn't have to. Please help.