after creting a graph builder when i run the the parametres the image of the product is not loading it shows error
Try searching for that file in your computer and see if it contains any data, or open it separately in snap.
The “V” icon for a band: 
indicates a “virtual” band. Virtual bands save a formula, which means there are limitation in how they can be used.
Have you tried creating “real” (e.g., non-virtual) bands?
There may be more helpful details for the error in the messages.log file (Help Menu will give you the location of the file).