Here're many software in market which are free or paid and free to try. You can download them in your PC and record your game play video in HD or regular format. Check out some websites which give you so.
wegame.com, fraps.com, taksi.com, gamecam.com etc
When you start recording game in your computer, the pc gets slow. Its good sense that you record it in lower pixels like 320x240 or bit above. If you want to record it in HD then your system must be higher processor like core i3, i5 or i7