Windows 7 - Game recording, Audio - Video lag in Windows Media Player

Here's the issue I've recently been having. I've begun doing video game Let's Plays in my spare time, and it was going well for the first little bit. However, when I reviewed the last two video recordings, the audio and the video weren't synced; the audio would play fine, but the video would be anywhere between thirty seconds to two minutes behind the audio.

I've tried reinstalling the recording program I use (Hypercam3), and I've tried restarting and reshooting the videos, but the same lag still happens. I've also tried reducing the length of my videos, but it hasn't had any effect on the lag. I don't know if the problem lies in the software or the media player. Any ideas on how I could try to fix this?