I have full wireless connection but can't connect wirelessly.

I had full wireless connection at home but recently moved back to France and have been in two different appartments since I moved. In neither could I connect to the wi-fi even though it says I have full connection. In the first house I was the only student who couldn't connect and had to use a borrowed cable. In my new proper appartment I'm still the only one who can't connect even though it's a private home network and I used the correct security key etc.

I am thinking some setting has been changed either by myself or by a programme to cause this problem that I havn't had in Paris before. (last year when I stayed here I connected instantly to the wireless in my appt) I just can't work out what I've done and I'm afraid to go too far changing things when I don't know what they do.

Suggestions would be much appreciated but simple instructions please. Any tech jargain and I most likely won't know what you mean .

I don't know what that is but I assume it does as the other girl who is renting here is able to connect without issue. I'm certain the problem is something inside my computer/internet setting!