Thank you for using answers.slingbox.com! I'm sorry to hear you are having trouble connecting to your Slingbox from your Windows 8 PC. I understand you have tried other web browsers as well, but all to no avail.
You will need to ensure you are using your computer in Desktop Mode. If it is not, it will not work with Watch on Slingbox.com. You can change your computer to Desktop Mode by hitting the windows key on your keyboard.
Have you received any error messages when attempting to connect on this PC? Also, do you know if there are any Antivirus softwares on the computer and what the names of them are, if any?
Below is a link to an article from our support site that may help troubleshoot this issue:
Hope I was able to help!
The Sling Moderation Team