Internet connection problem

I am having a problem with the internet on my laptop. It takes a long time to connect to the internet in my apartment block. This has been happening for the last month and 10 days (before this it was connecting fine). I use my laptop in my college and my apartment. When I connect to the internet in my college (or at home) it will connect to the internet straight away.

When I connect to the internet in the college and then go back to my apartment and connect to the internet it normally connects fairly quick, but if I didn't connect to the internet in the college it would take a hell of a lot longer to connect to the internet (anywhere from a an hour or two to nine + hours). During that time it will connect to the router but say limited/no internet access and then it will disconnect and repeat.

How I know something is wrong with my laptop (until recently I thought it was something wrong with the router) is because I can connect to the internet in my apartment straight away if I use Ubuntu (I have Ubuntu 11.04 on an external hard drive).

Why is this happening and can anyone help (please)?

I don't have access/permission to do anything with the router if that's the problem.