MacBook Pro won't load the login page of Wifi Hotspots... Any idea why it is so?

Hello!

I recently bought a Mac for my studies, and I'm already starting to regret it! I have to deal with a huge problem : I can't connect to any of the 3 Wifi Hotspots at College :

When I try to connect, the computer will detect the network, seems to connect to it but always fails to reach the login page of the Hotspot. (When I open chrome or Safari, There's a message telling me that I'll be redirected to the authentification page but it always ends with a "connection timed out" message.) Therefore, no acces to Internet.

This problem must come from my Mac. Every other device (including my IPhone) will successfully reach the Internet! I tried to change DNS addresses, didn't work either. I tried to reach the login page directly entering the IP address of the routeur, found in the Network Preferences... Failed again!

One last thing : even if it isn't perfectly stable, I can connect at home to my Box.

Any ideas? Thanks for your help!