Why can't I connect to the wireless network after the network password was changed?

Go to Control Panel → Network Connections, right click on your WLAN connection and select Properties from the context menu.

Click the Configure button next to the Wireless Network Adapter, and then open the Wireless Networks tab. Delete your network from the Preferred networks list.

After that, let Windows detect the network again and use your new WLAN key to connect.

Did the security mode change from WEP to WPA or vice versa? Try doing a factory settings reset and reconfigure your network... That should most likely solve your problem...

Can you specify the make and model of your router?! Netgear has some issues with some of the models...

Perhaps you think you have the right password, but in reality it isn't. So either log in to the router and verify it, or if you can't get into the router because you don't have that password, you need to reset it. If you need more help then post your router model.

I would also suggest that perhaps when the new computers were added, the the off-site tech may have flashed the firmware on your router and now some setting in the router setup isn't playing nice with your configuration/or adapter.