Uninstall your wireless driver
, reboot, let windows re-install it.
1. Go to Start Menu
2. Right click on My Computer
3. Click Manage
4. Click Device Manager from the list on the left
5. Click the + next to Network Adapters
6. Right click your Wireless Network Adapter
7. Click Uninstall
8. If a check box appears to delete the driver software for this device, check the box
9. Click OK
10. Restart your computer
11. Let Windows install the driver software
12. Find the newest driver software and install it from the Wireless Network Adapter's manufacturer site (if you need help with this, let us know)
Edit: Doing the above steps will require you to set up your wireless network on the computer affected. You will need your encryption key(s).