Thanks for using our answers forum! I'm sorry to hear that you are having this issue with Watch on Slingbox.com on your one PC. It's hard to say what could be causing the video to remain frozen, and it does seem like an issue with that one particular machine. I would advise clearing cache and cookies and/or trying a different browser.
Here is an article form our support site regarding system compatibility with Watch on Slingbox.com:
Hope this helps!
The Sling Moderation Team