The only other thing I have for you is bad connection.
The digital medium can get pretty picky. It's best not to use splitters or old cables, partly because older cables suck up interference but mostly just because the hardware is getting more and more picky about the exact nature of the signal.
There are several posts you can find through google on helping to reduce signal issues in a coax line.
This solution seems to have worked for this person. [Solved] TV Tuner, Low bit rate - general-discussion - windows-7