Technical Help Request

My windows machine is having video playback problems. Anything like YouTube, anything like Media Player playback, etc. is pausing every few seconds. I mean literally pausing every 3 or 4 seconds. I've tried a variety of formats and sources - it does this with CD's too - and they all behave exactly the same way.

Secondary problem: No sound. Not from speakers, not from headphones. Front jack, back jack, same silence. Every volume setting I can find is turned up and not muted. I'm stumped.