It seems that you are having some issues in order to get the connection to your Slingbox using a specific computer.
The fact that you are able to get the connection from other devices means that the Slingbox is a "healthy" unit. This situation allow us to narrow down the possible root cause to that specific computer.
With this in mind, I encourage you to check the following links in order to find the cause and the possible solution for this issue:
my problem has been SOLVED!
if you are using NOD32 v5 or another antivirus, even though you disable it or "temporarily disable it as-is the case with NOD32, it IS or COULD STILL BE ENABLED, BLOCKING THE STREAMING. that is the case with most current NOD32 v5 release. here is the fix:
Here's what you do (my setup is on Windows 7 64bit and the latest version of Firefox):
-Open the ESET main window-Open the Advanced Setup menu, which is done by clicking the green check in the upper right hand corner and then Advanced Setup
-Expand the Web and email section-Expand the Protocol Filtering sub section
-Click Excluded applications
-In the list that opens, put a check mark next to:
–C:\Program Files (x86)\Mozilla Firefox\plugin-container.exe–C:\Program Files (x86}\Sling Media\SlingAgent\SlingAgentService.exe
–C:\Program Files (x86)\Sling Media\SlingPlayer\SlingPlayer.exe