My father in law is having somebody steal his internet because he doesnt have password on it can anybody please help me out by telling me how to put a password on a ASUS WL- 520GC Router. his lost cd & instructions.

Follow these steps and you should be able to set up a password protected connection. (NOTE: You should use the cable that came with your modem as the connection will be lost until you reconnect to the wireless after setting up a password protected network. It is not mandatory but it helps to keep the connection to the router while you are setting this up.)
1. Open up your web browser and type 192.168.1.1 in the URL address bar and select enter. This should open up the web page for your router.
2.Input the user id and password. The default for both are admin.
3. The security setting should be under the Wireless menu option on the left of the window.
4. There should be an option to select medium or high securty levels. I would go with medium as it is easier to set up and should provide the security you are looking for.
5. There should be an input for a passphrase. Input a passphrase that is easy for you and/or your father in law remember as it will be needed to set up your wireless device on your desktop or laptop.
6. Select generate keys or it may generate them automatically when you type in the passphrase ( I am not sure since I don't own this particular brand of modem)
6. Write down the passphrase and 1 of the 4 keycodes generated to use later.
7. Exit your modem setup after saving your changes.
8. Go to Control Panel and select Wireless Networks
9. Double click on the wireless network connection
10. Select Properties
11.Select Wireless Networks tab
12.Highlight your wireless network and select Properties
13.Select the proper Network Authentication method (WEP)
14. Select the proper Data Encryption (TKIP)
15.Input one of the keycodes created in step 6
16. Close everything out and save.
17. Disable your device and then enable your device. This will cause it to reset. When it comes back up it should automatically connect to your network.

If you have to select WPA instead of WEP you will follow the same steps. Hope this helps. Here is a link to the online manual if you need it.

http://support.asus.com/download/download.aspx?SLanguage=en-us