I had a bit of a problem in the past. Disconnecting the power supply and phone cable for a couple of minutes was the only way to fix it. I don't think the routers supplied by Vodafone are very good. There is some discussion on the internet complaining about them.
I changed to a Netgear router, and the channel that the wireless broadcast on (I'd noticed that the signal always seemed to drop when a certain router in the area appeared on the list of available connections), and since then, no problems