My wireless network works just fine normally, I'm running a Linksys WRT54GL (http://www.newegg.com/Product/Product.aspx?Item=N82E168...). But when my friend brings his laptop over and starts it up, everything in our network ceases to function. Our home PC, my laptop, iPods, Xbox, other laptops, etc. -Nothing- can connect to the internet except if I plug them directly into the modem. This has happened twice already.
What I'm asking is, can a faulty network adapter or something similar cause a router to default and lose its settings? Because that seems to be happening here.
Next time see if you can connect your friend to the system via.
If there's no similar meltdown, it might suggest there's a fault in his wired ethernet adapter or your router.
The only similar circumstances I can think of were when a computer had previously been used with Windows Internet Connection Sharing and that (I think) had fixed the IP address -- that messed up connections with another computer. Solution was to uninstall Windows ICS.