Are you using Firewire of analogue - if the latter, check your leads - this may be the root of your problem.
What are your video overlay settings like - i.e how do DVDs etc play on your PC? If they play fine, you can def rule out anything to do with your PC settings and isolate it to the capture process.
Sorry if this sounds a tad lame, but I've learned the hard way that it's best to try and isolate the problem by asking dumb questions
