Black screen but sound and touch screen beeps seem to be ok.

From Garmin's knowledge base:

Question:
How do I perform a master reset on my nuvi 200, 205, 465, 500, 600, 700, 705 or 1000 series device?

Answer:
To perform a Master Reset on the nuvi 200, 205, 465, 500, 600, 700, 705, 1100, 1200, 1300, 1400 or 1600 series device:

Note: A master reset will erase all waypoints or Favorites and will restore your unit to the default factory settings. If you would like to back up your Favorites to your computer, you can find instructions to do so here.

Start with the unit OFF and unplugged from power
Touch and hold the lower right corner of the screen with an index finger or the eraser end of a pencil
Continue touching and holding the lower right hand corner of the screen then power the unit ON
Release the power button when the device powers ON
You will see a new message: Do you really want to erase all user data?
Remove your finger from the touchscreen when this message displays
Touch Yes
The device will automatically reset. Follow the on screen prompts then place your device in an area with a clear view of the sky until it acquires satellites.

Link Referenced In This Article:

http://iqc.garmin.com/eCustomer/KODSelfService/request.do?create=kb:garmin&view()=c%7B51c35d50-3dbf-11df-e655-000000000000%7D

Most likely a defective LCD display. If the unit was dropped, the LCD ribbon cable might have pulled slightly out of the connector on the PCB board.