Might be an idea to update your drivers to the latest version if you have a NVIDI GeForce graphics card installed before using any conversion software.
I tried various software and found myself staring at the 'blue screen of death' right at the end of a long wait for the conversion to take place, until I updated my drivers.
Although it might of been a combination of drivers and the fact I was unlucky enough to have Windows Vista installed at the time!