You have two possibilities here:
- The LVDS cable is loose or bad
- The driver logic on the back of the LCD has become disconnected from the LCD panel
Did you bang your laptop? If you had its likely the LCD is gone and you will need to replace it.
I would start with the idea its just a loose cable. Pop the bottom cover off and inspect the LVDS cable connector connection to the main logic board. Review this IFIXIT guide Installing MacBook Pro 13" Unibody Late 2011 Display Jump to Step 14 to find it. Does it look OK? also do you see any corrosion or other water damage? If it looks OK go back to Step 1 and follow the guide to the end (Step 20). As this guide stops at removing the lid assembly you will need to jump to a different guide for the rest or the process. Follow this guide Installing MacBook Pro 13" Unibody Mid 2009 Front Display Glass from Step 15. Sorry to say it to doesn't get you the whole way either but the last steps are self evident. You will need to remove the LCD mounting screws and very carefully remove the panel and the still attached cables. On the back side you will see the LVDS cable connection sometimes this connector needs to be cleaned & reseated. carefully connect things back so you can check the connections. Only at this point can you figure out if the LVDS cable it's self is bad or the LCD panel needs to be replaced.
If you know you banged your laptop you may opt to just replace the entire lid assembly.