Hi bobkwok, here are some options for troubleshooting.
1. When I watch TV on the laptop that I used for doing the initial Slingbox setup,
the picture is in 4x3 mode and not 16x9. I don't seem to be able to change to HD mode
on the Slingbox.
Try to use Watch.slingbox.com once you connect to your Slingbox look at the bottom of the page, in the right there is an option that says "Auto", there you can change the video quality.
2. WHen I watch TV on another laptop, I got sound but no picture, just a green screen.