Error 403 on new network

Hello all, i come to you with an error which has had me stumped for a few days and i cannot seem to find the problem.

My girlfriends dad is a College Teacher, and he has had a laptop provided by them for a good 3-4 years.

He had the college network on his laptop before i installed his home broadband and the new home network. So, seen as though its been the holidays he hasnt been into college alot.

But anyway, he took his laptop into work on Monday, and reconnected to their network using wireless (uses a cable at home, dont think this makes much difference) and after coming home, my girlfriend tried to connect to the internet and it automatically tried to load up " //portal" (which is college staff homepage).

She tried to navigate away from the page, but everytime she tried it gave her error 403, as described here Error 403

I have managed to get rid of 103instances of spyware and 3 viruses, but still nothing. I have closed everything down in task manager, and disabled windows firewall etc, it still says the same.

It IS giving valid details, eg IP etc. According to the error, its the modem which isnt allowing them to use the internet at home.

But.. this is where it gets wierd, you know of portable software right? Well, i took portable Mozilla Firefox around to her house, and to my suprise it works.
So i have placed the portable Firefox folder on there desktop and they will have to use this for the time being.

But my girlfriend is still unable to use MSN Messenger because of this, and the installed browsers still do not work, only Portable.
Is there something blocking it perhaps? I have no idea myself, but it doesnt allow installed software to access the internet, only portable applications.

Hope somebody is able to help, and hope i covered in enough detail.

PS : When her dad takes her laptop to work, IE and MSN etc all work through the college network.


Thanks, Jamie.