Why fewer channels than on my tv

I have a tv tuner built into my HP laptop. I have a splitter from my converter box attached to rooftop antenna. After the digital conversion here in the U.S., I got 12 channels on my laptop. Now I get four. My television gets more. Why the difference between the tv and laptop when they are both from the same rooftop antennna?

And if anyone knows why I am getting fewer channels than before, I'd like to know that. I was told a few weeks ago that the tv stations were only at half power, were supposed to go to 100% soon and then I'd get more channels.

You need to add the subchannels manually; the problem we all have with micrcosoft and the Digital over the air subchannels that they do not get the TV listing instead you get no data available listing for these subchannels. Here's a link with instructions on how to set up the subchannesl. These are, I think, the channels you're not getting in Windows Media Center. The subchannels are like 7.2, 7.3 and so on. Adding Sub-channels to Vista Media Center