I would try with a different browser or with the standalone Slingplayer (http://download.slingmedia.com/player/pc/SlingPlayer-2.0.4-Setup.exe or http://download.slingmedia.com/player/mac/SlingPlayer-1.0.10.dmg)
I'm sorry to hear your having trouble accessing your Slingbox. It sounds like it may be either your Internet connection or how your Slingbox is connected to the Internet. What I would suggest is to eliminate any SlingLinks or Wifi bridges and perform a speed test on your computer that is on the same network as your Slingbox. I would recommend taking a look at the link below for the speed test:
I hope you find this information helpful!
Have a great day,
The Sling Moderation Team