Can't see Network Available

Hi all, I've got a network at home with 2 wireless PCs, a wired PC and a
wireless laptop (all XP). I recently bought a new laptop with Vista, turned
it on and it found our network, connected and all was fine. The next day, I
turned it on again and it doesn't see the network. it sees neighbours
networks, but not ours. I have tried resetting the router, and that has no
effect. As a last resort, I re-installed Vista. First time I loaded up, I
could see the network again. Next day...guess what? Can't see our network.
I just can't figure out what is happening. It is almost as if once it is
connected once, it just won't see the network again. SSID is turned on, and
the laptop works fine if I wire it to the network, so I can't see what on
earth is happening!

Any ideas?

Thanks