The problem could be either the Router Wireless settings have somehow changed or that the Wireless WLAN module is broken / defunct. If broken then you are probably going to need a replacement router for wireless access!
First check is to determine if the wireless settings have changed by logging onto the router which requires a router Admin userid and password to gain access. As this process is likely to be somewhat technical it may be worth seeking assistance from whoever initially setup your router.
For example, using your Computer web browser enter the web address:
http//:192.168.1.1
This should present the Router logon page. I believe The default userid name is 'admin' and password 'admin' but this may have changed depending on how it was first configured. The userid / password maybe be printed on the side of the router along with other details for the wireless configuration such as SSID name / Password.
Further examples of the router menu setup system are available here:
http://www.bryana.talktalk.net/public/DSL-2640R%20User%20Guide.pdf