Internet browsers: they freeze and then get back and then freeze again...

Dear experts,

First of all, I apologize for my English. If something seems a little confusing, please tell me, and I will try to make it clearer.

I have a Dell Inspiron 5520, Intel core i5, 8GB of RAM memory, Windows 7 Home Premium, 64bits, 2,5GHz.
I am also running Microsoft Security Essencials.

I've been experiencing some issues with Internet Explorer 9, Mozilla Firefox 18.0.2 and Google Chrome: very often (each 40 seconds) navigation gets frozen - sometimes I can't click any clickable link from the pages where I am, sometimes I can, but they won't open. It behaves as if it was loading. Sometimes I can go page up or page down, sometimes I can't; I am able to open a new tab and type another address; but in every situation, when I hit Enter to load the page, it won't go. The page remains as if it was loading, but nothing is done. This lasts about 10 seconds, and then everything is fine again for the next 40 seconds.

I thought that could be something with the connection, but other programs using internet work well.

Do you have any idea of the cause of that? It is very annoying and I don't really know what to do.

Thanks in advance!
All the best!