Not all computers can connect to Wifi all the time

I have Orange Broadband with a Wanadoo Livebox and after this Christmas we have ended up with 4 laptops, a Wii, an Iphone and an Ipod Touch all fighting for a Wifi connection. I have temporarily turned the security off as sometimes that can cause problems.

At this very moment in time all 4 computers, the Iphone and the Ipod can connect to the internet (haven't tried the Wii) but sometimes some will be on the internet yet if you try to connect with another computer it will just refuse to connect and the only way to rectify this seems to be to restart the router. Any idea what the problem is?

Sounds like some devices have the same IP addresses.

it's all on automatic

So was my speedtouch 585 but it still managed to assign the same ip to 2 laptops from time to time.