It sounds like you have the "white screen of death" (I made that up) non-responsive screen...meaning you cannot enter data or make the unit respond to finger or sylus presses. There is a procedure for getting the screen back to normal, provided there are no other software or electronic issues.
Try these steps:
1. Turn off the Nuvi.
2. Hold the upper-left of the screen while turning power on.
3. Release the Power
button when the Garmin screen appears.
4. Continue to hold the upper-left corner of the screen for 30 seconds, until a white screen with "Press dot
5. Press dot and that should get you back to normal.
Also, you may to need perform a hard reset for your unit to clear out any erroneous data.
These GPS units can be reset by holding the Power button for 10-15 seconds to completely shut the unit down. Then, do the same procedure for 10-15 seconds again, to power it back on.
It would be best to assure the unit has external power, and hopefully a full battery charge, for best results. Also you can download a complete manual from this link for more info:
Starting on page 47 of the manual in the appendix, it tells you about calibrating the screen (problem discussed above), updating software, and clearing user data.
If these steps don't bring your unit back to life, you may need to contact a regional repair facility or the factory for service.
Let me know how this turns out, and if I can help you further.