Which network card do you have? Different cards have different driver software that presents different configuration and diagnosis options. In your wireless card software you should first ensure the wireless is turned on. If the software gives you the option, try release/renew of the IP. If it doesn't, download
MyIpConfig (open source freeware) and you can accomplish the renewal. Ensure the IP is correct for a DHCP handout from your router. Also, double check your encryption key and signal quality.
A soft reset never hurts too.
