Not connecting to wireless network

My mum's got a sony vaio running Win7 pro 64 and whenever she trie to connect to our network it just doesn't.

I open the list of available networks then click on our one and then click connect. Then the list disappears and that's it. It doesn't ask me to enter a password, and it doesn't connect. It does the same on every network i've tried it on. It used to work fine but has been like this for a few weeks now.

My dad's got the same laptop and he hasn't had any problems. I've tried reinstalling the driver but it still does it.

Has anyone heard of this before?

I don't even get as far as being asked to enter a password. As soon as i click on the Connect button the list just disappears and i have to start again. The wireless symbol next to the clock has a little yellow star on it.

I've been able to see the security key on my dad's laptop, but i already know what that is anyway.

On my mum's laptop if i go to Manage wireless networks it doesn't list anything there, and when i click on the Add button nothing happens - the button is depressed but nothing loads up.

Nope. We bought the laptops together almost a year ago - they have identical specs, and we haven't had any problems since then, so have had no reason to reinstall Windows.