When your flash is grossly overexposing your pictures…
- The flash is not seated correctly, or the contacts are dirty
- The flash is set to MAN (manual), instead of TTL
- You are using + Flash Exposure Compensation (or on a Nikon, also Exposure Compensation).
- You are simply too close.
Those are four obvious starting points.
Here is me, pictured by David Honl in Las Vegas the other evening. Using a Leica X1 with off camera flash equipped with CTO gel and Honl Photo Traveller 8 softbox.