Hi, My name is Eric Moyers. I am a Network Support Engineer in the Cisco Small Business Support Center. Thank you for using the Cisco Community Post Forums.
The WRT600N is one of our Consumer Routers. You should look here for help with that device.
http://homesupport.cisco.com/en-us/wireless/lbc/WRT600N/
If this had been on of our devices, I would first suggest making sure that the FW is up to date. Then doing a factory reset and manually reconfiguring the device. If that does not work, I would call the Consumer Support line 1-800-326-7114
Thanks
Eric Moyers
Cisco Network Support Engineer
SBSC Wireless and Surveillance SME
CCNA, CCNA-Wireless
1-866-606-1866