OK. A few things.

- I assume your Sitecom is the only router between your computers and your ISP (you don't have multiple routers configured)

- just as an aside, do you know that your wireless computers are, in fact, connected to your router not an open wireless network?
- Do you have cable modem on other end? you use DSL or cable or other?

Best steps i think
- Turn off router and computer
- Restart router give a minute or two (and test from wireless while down and back up they talk to it ok)
- Restart computer. Now run the Network wizard again to let it reconfigure settings

Still no joy after restarts unfortuantly. The wireless is deff conected to my router and the router is connected by telephone cable.

As I say I am convinced it is computer related.