it means your video card crashed.
it used to be that when your video card crashed it crashed your whole system. but now they made it so the video card driver resets and you can continue using your computer.
to fix it crashing all the time get a different driver. best to use a new one but older sometimes works.
if you have an amd/ati card go here http://support.amd.com/us/gpudownload/Pages/index.aspx
if you have nvidia go here. http://www.geforce.com/Drivers