If you can communicate to the PiCapture board using PiVideo then it is very likely that it is not the problem.
We have found that the Raspberry Pi GPU is very sensitive to power conditions when power is first applied and it is initializing. When this happens, the ARM processor can be running properly but some GPU functions including the camera interface aren’t working.
The best suggestion I have is to check the power supply, and perhaps try another power source. The most important thing is that there is no voltage drop at initial power-on when the demand is high.