Okay - let's upgrade the firmware of the router - this may be why the slingbox is not recognized.
Save this file to your desktop - this should be done over a wired connection, not wireless:
Once it is save, open Internet Explorer and enter this address:
A login screen will appear - leave the username blank and enter admin for the password. Once logged in, click Administration, then Firmware Upgrade.
Select your downloaded file, then Upload. The router will restart and can't be interrupted while the upgrade is happening.
Once the router restarts, and you are back online, press and hold the rest button on the back with a pen for 15 seconds, then release.
When you are back online, try the Slingbox software again. Any luck?
With the reset, wireless settings are erased - use these steps to set them up again:
Login to the router again.
Click Wireless at the top of the page. Change the Network Name (SSID) to anything you would like, just something unique that you have not used before - this will be the name of your wireless network. It's best to not have any spaces in the network name.
Next, click Wireless Security in the submenu just below Wireless. Change the security mode to WPA-Personal. You will see a passphrase/pre-shared key box - this is your wireless password. Enter a password XXXXX at least 8 characters, then save the settings.