Please follow the steps in order resolve the issue.
1.Refer to the link http://homesupport.cisco.com/en-us/wireless/linksys
2.Enter the model number and hardware version and download the latest firmware. Save it on the desktop.
3.Open web browser and type 192.168.1.1 and hit enter.
4.If you have not changed the default password then type admin as password and leave the username blank.
5. In the router setup page click Administration and then click Firmware.
6. Click browse and select the file you have downloaded and hit Upgrade.
7. Turn off the router for 30 seconds once the upgradation is over. Switch it on after 30 seconds.
8. Open web browser again and type 192.168.1.1 and hit enter.Enter the password.
9.Click Wirless and fill the sections as mentioned
*Wireless Network Mode: Mixed
*Wireless Network Name: Any name as per your choice.
*Wireless Channel:6-2.437 GHz
*Wireless SSID Broadcast: Enable and click Save settings.
10. Now click Wireless Security and fill the required fields:
*Security Mode: WPA Personal
*WPA Algorithm: TKIP
*WPA Shared key: Any ten digit number (please note it down, as you will require this to connect your wireless devices). Then click Save settings.
11. Click Advanced wireless settings and fill the fields as:
* Beacon Interval: 75
* Fragmentation Threshold:2306
* RTS Threshold:2307 and click Save settings.
Turn off the router for 30 seconds and switchit on. Use the shared key as the password whenever you want to connect any wireless device.
I hope this will resolve the issue.