My laptop crash and I put windows back on and now my laptop does not show that I have a wireless network anymore. How do I fix it

Control Panel > Network and Internet> Network and Sharing Center>
Now on the left hand side, click on Manage Wireless Network. And see if you can find out what's wrong with it. Usually you just disable it.
I'm assuming you have vista. If xp it's easier.
Last resort, System Restore, tada, and you get everything back to its original shape, losing all the data from that date forward.