I have a mid-2008 aluminium unibody Macbook, and a WiFi dongle on the 3 network. I've had this set up for just over a month, and never had any problems. The network was set up to connect automatically, although it was password protected. This morning everything was working fine, internet at a reasonable speed, but I put my Macbook to sleep for a couple of hours then when I came back it wouldn't connect to the network automatically. I put the password in and it took longer than normal to connect, but did, but then the internet was really slow (and I mean really slow, it took 20 minutes to load Google). Over the next few hours the network connection repeatedly cut out for no discernible reason, and now it won't connect at all. I've restarted the dongle and my Macbook multiple times, but it just refuses to connect automatically, and now whenever I try to connect I enter the password and just get a connection timeout. I really don't understand, I haven't updated or changed any programs, system files, etc, and my flatmate's Windows PC has had an uninterrupted connection all day. I think it must have something to do with Airport, but I really have no idea. Any ideas?

Thanks in advance.