It is always better to set power from the design screen as it has more resolution vs the override which is scaling from current (not ideal, but it works). The override is really for when you load an existing G-Code file and need to change it.
So anyway, to answer your question. Increase the speed?
Some of the laser modules don't like running at lower levels, the current regulator isn't capable of switching on fast enough (or the diode doesn't reach the necessary junction voltage) so you get no output. One trick is to increase the minimum power to 50 so the laser is always getting some voltage/current and then it responds faster and perhaps more linear. It will reduce the life of the diode though, so keep that in mind.