Hayes Sole Disk Brake sudden loss of pressure. I braked hard today and felt the pressure in my disk brake drop very suddenly. 

Since that point the brake has not been working with no action at the calliper and little  pressure in the lever but not spongy.

Any one know the likely cause and whether a bleed might fix. 

I can't see any evidence of fluid leakage.
Sounds like a major fluid loss, somewhere. Check around the hose joints, and the brake levers and calipers for fluid leakage. If not, it's probably a blown piston seal, which in rare cases can leak, but reseal under low fluid pressure.