OV5642 does not work issue
If all connections are correct, then I support @RogerRowland comment - the sensor needs to be initialized/configured before it will work. I used one of the Omnivision sensors without configuration (did not know there should be one) and I had the signals all working, however, the pixel data was not correct. In your case, it may be possible that the configuration is necessary before getting any output signals.

The SCL and SDATA pins are used to configure the sensor. It is a pretty much I2C interface. There should be a list of registers that must be configured for proper functionality.

EDIT:

If you are sure that your sensor can show signs of life without configuration, then the sensor/board seems to be dysfunctional. I would still try to do some reads/writes to the registers, or at least, reconfigure the clock register - it looks like the chip can take a wide range of clock frequencies (6-54MHZ). Try contacting the vendor.