I personally use Fraps It’s a recording software that record any DirectX image on your screen, there is a small demo, that allow you to record some sec of gameplay. Now if you plan to record more then a few sec you need to buy it. It’s not very expensive and is a life long license.
If you want to try free there is some alternative like:
My main recommendation is is the free recording application included with xfire. Once you have Xfire install go in the Xfire option to activate it and choose two keys to launch it. Xfire video recording does a good job considering it’s free and doesn’t put watermark on your video.
There is also Camstudio. It is an open source recorder (meaning it’s free and developed for free). It work really well but it’s not compatible with some sound card. So, maybe a solution to this would be to record your computer sound with the software Audacity. So when it comes to editing your video you can can try to make fit both the sound and images. (This trick might also be useful apply to the following software.)
There is GameCam but as far as I know the trial version doesn’t record sound but does a good job recording some game. I had trouble in the past with specific games.
HyperCam The demo of this software allow you to record 10 min. It’s seem a good recording software, but it might be a little complicated for those without experience in the domain.
Here are the tutorial video of fraps which will help you guide using it. [Tutorial] Record PC Games - Part 1 of 2: Fraps - YouTube [Tutorial] Record PC Games - Part 2 of 2: VirtualDub - YouTube
Hope this helps you.