A message comes up saying it can't find a valid certificate.
PEAP provides more security in authentication for 802.11 wireless local area networks that support 802.1X port access control.
If this occurs, you can manually configure the wireless network.
In first phase the client authenticates the server using a TLS -Transport Layer Security, certificate-based mechanism.Make sure your Wi-Fi is turned on by looking at any button or status light indicator.Typically, the light will be either blue or green when enabled.Check all wireless access point (AP) or wireless router ports to ensure that Ethernet cables are inserted tightly and link status LEDs are green at both ends.
If not: Once your wireless client has a valid IP address, use ping to verify network connectivity.
You can quickly setup a wireless network using the wireless configuration feature in Windows XP.