Dell A6100 cannot connect to my new network

I've just changed my internet from wifi to broadband wifi. I am running a dell computer:  "Dell OptiPlex 3020 Small Form Factor". It has no network card, so I'm using dell USB wifi adapter model: A6100. It can connect to my old internet, but not my new internet. My phone can connect to my new internet, no problem, but not my computer. I've tried to re-install the A6100 adapter. Doesn't work. I've also tried to split my router into both 2.4 GHz and 5GHz. Doesn't work either. 

What should I do? Do I have to change my wifi adapter to another one? Please help, thank you