Great post on your issues. Wish more folks would include more information like you did.
I will try and walk you through a few things. If this doesn't help try hitting me up live here and maybe we can resolve it.
Do a hard reset on your Slingbox. Afterwards make sure that both the power and network lights are on solid
Run your Windows SlingPlayer program, assuming it's 2.0.4.x, and see if it shows you that you have an unconfigured Slingbox. If not then there is a problem.
If so then tell it you want to set it up and see how far you get. If you get to the scan channels and it doesn't work or gives you an error message let me know the exact spot that it does.
My ant in port doesn't work either. If i plug a tv into the cable it works just fine but when I plug it into the slingbox the it doesn't feed any video. I can use the s-video but the sound doesn't work on the s-video. I tried the system reset and I was able to reconfigure the device but it still says weak or no video signal when I have the cable connected. What's wierd too is that when I go into the setup assistant and click on set up your slingbox, it says that this slingbox was not originally designed to be used in the USA. You may not be able to configure this slingbox for some devices in this new location. I bought it at Best Buy in Massachusetts and it was working fine for two years until it just stopped working. Any ideas?