If the record function is producing empty files (i.e. files that are only 0 kB in size), this is likely because the sound is not being recorded along with the picture. In most cases, this problem can be fixed by switching the audio driver.
But before switching the driver, try the following:
To change the audio driver, follow these steps:
The USB video converter should now be "active", and you should be able to record normally.
If the recording still doesn't work, set the recording quality from "Very high" to "High" and try again. In the record dialog, enable "Automatic scene recognition" (bottom right, above "Start video editing").