you might need an amplifier. Sometimes(maybe a lot of times, not really sure), signal coming into the house from the cable company is just strong enough to where you can connect to the internet or get a good tv signal. What happens when you use a splitter is that for every splitter you connect in series, it basically takes a bite out the strength of that signal. So, when using a splitter, the signal that comes out of it, will always be weaker than the one coming in.
A better quality splitter might not weaken it as much, but since a weaker signal simply comes with the nature of a splitter, I doubt that a better one will help much. All that being said, I'm sure that an amplifier would fix your problem, but it's probably not your only solution, and it's probably not your cheapest either. So you might want to check out radio shack, they probably have something there that would help you out.