Please check your dscr.c file again to make sure everything is correct. After that you could use oscilloscope to check if the image sensor outputs data and if FV/HV works fine.
The necessary changes to add a different resolution/frame rate is mentioned in the below link. Please make sure that you have followed the instructions.
The page is no more available. Can you please send a copy of the same or provide another link where i can find it?
Please provide the OV7670 project folder?
I hope will help me.