First, what are you using? wireless router...with wpa/wep/MAC filtering?
If your network shows as "secured" you will need to enter your key after you click "connect to network" You can recover this key from your xp machine (see attached)
Here is an easy fix if the above info/key is unknown:
step 1
there should be a little reset "hole" on router- usually in the back.
Push it in with paperclip, or push pin and hold it there for 30 seconds.
step 2
Unplug power from modem and router
step 3
restart notebook/power up modem and router
step 4
You should now see your unsecured network (linksys/netgear/Belkin/D-Link) click connect to your network (name of router)
note- In the event your internet is down you will still see the network, but you will not be able to connect.
if you are set up for WEP/WPA secured network, you can "reset" the connection by powering down the router/modem and powering them back up. DO NOT RESET THE ROUTER as this will restore the factory default settings and wipe out configured settings such as encryption and filtering.